{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,18]],"date-time":"2026-03-18T09:29:46Z","timestamp":1773826186211,"version":"3.50.1"},"reference-count":45,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2026,3,17]],"date-time":"2026-03-17T00:00:00Z","timestamp":1773705600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"King Faisal Specialist Hospital & Research Centre project","award":["RAC# 2190-002"],"award-info":[{"award-number":["RAC# 2190-002"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Programmed Death-Ligand 1 (PD-L1) promotes tumor progression through several mechanisms, including its intrinsic effect on breast cancer cell proliferation via the S-Phase Kinase-Associated Protein 2 (SKP2)\u2013p21Cip1\/p27Kip1 (SKP2-p21\/p27) axis. However, the specific regulatory signaling through which PD-L1 influences the SKP2\u2013p21\/p27 axis to drive cell proliferation remains unclear. To investigate how PD-L1 mediates SKP2-dependent proliferation, proteomic analyses, gene-expression manipulation via knockdown or overexpression, Western blotting, quantitative immunofluorescence, colony-forming assays, real-time cell analysis, and Xenograft-derived cells were used. Proteomic data analysis identified several PD-L1 downstream targets as potential candidate regulators of the SKP2\u2013p21\/p27 axis and activators of the PI3K\/AKT pathway. Candidate screening by gene knockdown, followed by analyses of SKP2, p21, and p27 protein expression, revealed Livin and Galectin-1 as upstream regulators of the SKP2\u2013p21\/p27 axis. Moreover, Western blotting and quantitative immunofluorescence in three breast cancer cell lines confirmed that PD-L1 is an upstream regulator of Livin, Galectin-1, and SKP2 protein expression. Mechanistically, Livin and Galectin-1 enhanced AKT phosphorylation (Ser473) to sustain PI3K\/AKT pathway activation in a positive feedback loop to upregulate SKP2 expression. Functional assays, including colony-forming assays and real-time cell analyzer, demonstrated that Livin and Galectin-1 are critical for PD-L1-mediated, SKP2-dependent proliferation. These findings were corroborated in vivo using xenograft-derived cells. Overall, these findings delineate a tumor-intrinsic signaling axis in which PD-L1 upregulates Livin and Galectin-1 to sustain PI3K\/AKT activity and drive SKP2-dependent cell proliferation. Targeting Livin and\/or Galectin-1 may provide a rational strategy to disrupt PD-L1-associated proliferative signaling and improve combinatorial therapeutic approaches in breast cancer.<\/jats:p>","DOI":"10.3390\/ijms27062741","type":"journal-article","created":{"date-parts":[[2026,3,17]],"date-time":"2026-03-17T16:20:14Z","timestamp":1773764414000},"page":"2741","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Tumor-Intrinsic PD-L1 Promotes Breast Cancer Proliferation Through Livin and Galectin-1-Mediated Regulation of SKP2 Expression"],"prefix":"10.3390","volume":"27","author":[{"given":"Marwa","family":"Elfoly","sequence":"first","affiliation":[{"name":"Innovation and Research, King Faisal Specialist Hospital & Research Centre, MBC 03, P.O. Box 3354, Riyadh 11211, Saudi Arabia"},{"name":"Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2124-8550","authenticated-orcid":false,"given":"Ayodele","family":"Alaiya","sequence":"additional","affiliation":[{"name":"Innovation and Research, King Faisal Specialist Hospital & Research Centre, MBC 03, P.O. Box 3354, Riyadh 11211, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Amal A.","family":"Al-Hazzani","sequence":"additional","affiliation":[{"name":"Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2150-5297","authenticated-orcid":false,"given":"Monther","family":"Al-Alwan","sequence":"additional","affiliation":[{"name":"Innovation and Research, King Faisal Specialist Hospital & Research Centre, MBC 03, P.O. Box 3354, Riyadh 11211, Saudi Arabia"},{"name":"College of Medicine, Al-Faisal University, P.O. Box 50927, Riyadh 11533, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3297-3996","authenticated-orcid":false,"given":"Hazem","family":"Ghebeh","sequence":"additional","affiliation":[{"name":"Innovation and Research, King Faisal Specialist Hospital & Research Centre, MBC 03, P.O. Box 3354, Riyadh 11211, Saudi Arabia"},{"name":"College of Medicine, Al-Faisal University, P.O. Box 50927, Riyadh 11533, Saudi Arabia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,17]]},"reference":[{"key":"ref_1","first-page":"7","article-title":"Cancer statistics, 2019","volume":"69","author":"Siegel","year":"2019","journal-title":"CA Cancer J. Clin."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"261","DOI":"10.1002\/jcb.20690","article-title":"Cell cycle control in breast cancer cells","volume":"97","author":"Caldon","year":"2006","journal-title":"J. Cell. Biochem."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"43124","DOI":"10.18632\/oncotarget.8988","article-title":"Wnt-beta-catenin pathway signals metastasis-associated tumor cell phenotypes in triple negative breast cancers","volume":"7","author":"De","year":"2016","journal-title":"Oncotarget"},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Dong, P., Xiong, Y., Yue, J., Hanley, S.J.B., and Watari, H. (2018). Tumor-Intrinsic PD-L1 Signaling in Cancer Initiation, Development and Treatment: Beyond Immune Evasion. Front. Oncol., 8.","DOI":"10.3389\/fonc.2018.00386"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"116203","DOI":"10.1016\/j.biopha.2024.116203","article-title":"Tumor immunotherapy resistance: Revealing the mechanism of PD-1 \/ PD-L1-mediated tumor immune escape","volume":"171","author":"Cui","year":"2024","journal-title":"Biomed. Pharmacother."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"4047","DOI":"10.1038\/s41388-019-0700-2","article-title":"WNT signaling modulates PD-L1 expression in the stem cell compartment of triple-negative breast cancer","volume":"38","author":"Castagnoli","year":"2019","journal-title":"Oncogene"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1402","DOI":"10.1002\/ijc.30834","article-title":"PD-L1 promotes OCT4 and Nanog expression in breast cancer stem cells by sustaining PI3K\/AKT pathway activation","volume":"141","author":"Almozyan","year":"2017","journal-title":"Int. J. Cancer"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"161","DOI":"10.1186\/s12935-024-03354-w","article-title":"PD-L1 intrinsically promotes the proliferation of breast cancer cells through the SKP2-p27\/p21 axis","volume":"24","author":"Elfoly","year":"2024","journal-title":"Cancer Cell Int."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"751","DOI":"10.1002\/ijc.22703","article-title":"Expression of B7-H1 in breast cancer patients is strongly associated with high proliferative Ki-67-expressing tumor cells","volume":"121","author":"Ghebeh","year":"2007","journal-title":"Int. J. Cancer"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"217","DOI":"10.1016\/j.lungcan.2004.11.002","article-title":"Detection of autoantibodies to livin and survivin in Sera from lung cancer patients","volume":"48","author":"Yagihashi","year":"2005","journal-title":"Lung Cancer"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"85","DOI":"10.1093\/annonc\/mdg002","article-title":"Expression and prognostic significance of LIVIN, SURVIVIN and other apoptosis-related genes in the progression of superficial bladder cancer","volume":"14","author":"Gazzaniga","year":"2003","journal-title":"Ann. Oncol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1552","DOI":"10.1038\/bjc.2014.453","article-title":"Fascin is involved in the chemotherapeutic resistance of breast cancer cells predominantly via the PI3K\/Akt pathway","volume":"111","author":"Ghebeh","year":"2014","journal-title":"Br. J. Cancer"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"168","DOI":"10.1016\/j.canlet.2006.09.024","article-title":"Livin\/ML-IAP as a new target for cancer treatment","volume":"250","author":"Liu","year":"2007","journal-title":"Cancer Lett."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"307","DOI":"10.1016\/j.ctrv.2013.07.007","article-title":"Unraveling galectin-1 as a novel therapeutic target for cancer","volume":"40","author":"Riveiro","year":"2014","journal-title":"Cancer Treat. Rev."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"241","DOI":"10.1016\/S1535-6108(04)00024-8","article-title":"Targeted inhibition of galectin-1 gene expression in tumor cells results in heightened T cell-mediated rejection; A potential mechanism of tumor-immune privilege","volume":"5","author":"Rubinstein","year":"2004","journal-title":"Cancer Cell"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1107","DOI":"10.1158\/0008-5472.CAN-12-2418","article-title":"Targeting galectin-1 overcomes breast cancer-associated immunosuppression and prevents metastatic disease","volume":"73","author":"Croci","year":"2013","journal-title":"Cancer Res."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Su, Y.L., Luo, H.L., Huang, C.C., Liu, T.T., Huang, E.Y., Sung, M.T., Lin, J.J., Chiang, P.H., Chen, Y.T., and Kang, C.H. (2020). Galectin-1 Overexpression Activates the FAK\/PI3K\/AKT\/mTOR Pathway and Is Correlated with Upper Urinary Urothelial Carcinoma Progression and Survival. Cells, 9.","DOI":"10.3390\/cells9040806"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Su, Y.C., Davuluri, G.V., Chen, C.H., Shiau, D.C., Chen, C.C., Chen, C.L., Lin, Y.S., and Chang, C.P. (2016). Galectin-1-Induced Autophagy Facilitates Cisplatin Resistance of Hepatocellular Carcinoma. PLoS ONE, 11.","DOI":"10.1371\/journal.pone.0148408"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1212","DOI":"10.1158\/1535-7163.MCT-16-0690","article-title":"A Novel Galectin-1 Inhibitor Discovered through One-Bead Two-Compound Library Potentiates the Antitumor Effects of Paclitaxel in vivo","volume":"16","author":"Shih","year":"2017","journal-title":"Mol. Cancer Ther."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"35804","DOI":"10.18632\/oncotarget.16208","article-title":"Binding of galectin-1 to integrin beta1 potentiates drug resistance by promoting survivin expression in breast cancer cells","volume":"8","author":"Nam","year":"2017","journal-title":"Oncotarget"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"E4820","DOI":"10.1073\/pnas.1609135113","article-title":"Nuclear repartitioning of galectin-1 by an extracellular glycan switch regulates mammary morphogenesis","volume":"113","author":"Bhat","year":"2016","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1179","DOI":"10.1080\/15384047.2020.1838032","article-title":"Obesity and metabolic syndrome related macrophage promotes PD-L1 expression in TNBC through IL6\/JAK\/STAT pathway and can be reversed by telmisartan","volume":"21","author":"Wang","year":"2020","journal-title":"Cancer Biol. Ther."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"377","DOI":"10.1038\/ncb0409-377","article-title":"Skp2: Caught in the Akt","volume":"11","author":"Ecker","year":"2009","journal-title":"Nat. Cell Biol."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1413","DOI":"10.1016\/j.cellsig.2013.03.012","article-title":"Livin promotes progression of breast cancer through induction of epithelial-mesenchymal transition and activation of AKT signaling","volume":"25","author":"Li","year":"2013","journal-title":"Cell. Signal."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"506","DOI":"10.1038\/s41419-020-2701-z","article-title":"PD-L1 promotes tumor growth and progression by activating WIP and beta-catenin signaling pathways and predicts poor prognosis in lung cancer","volume":"11","author":"Yu","year":"2020","journal-title":"Cell Death Dis."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1284","DOI":"10.1038\/s41418-020-00651-5","article-title":"KPNB1-mediated nuclear translocation of PD-L1 promotes non-small cell lung cancer cell proliferation via the Gas6\/MerTK signaling pathway","volume":"28","author":"Du","year":"2021","journal-title":"Cell Death Differ."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"e131458","DOI":"10.1172\/jci.insight.131458","article-title":"PD-L1 tumor-intrinsic signaling and its therapeutic implication in triple-negative breast cancer","volume":"6","author":"Chen","year":"2021","journal-title":"JCI Insight"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Ghomlaghi, M., Hart, A., Hoang, N., Shin, S., and Nguyen, L.K. (2021). Feedback, Crosstalk and Competition: Ingredients for Emergent Non-Linear Behaviour in the PI3K\/mTOR Signalling Network. Int. J. Mol. Sci., 22.","DOI":"10.20944\/preprints202105.0367.v1"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"99901","DOI":"10.18632\/oncotarget.21914","article-title":"PD-1\/PD-L1 interaction up-regulates MDR1\/P-gp expression in breast cancer cells via PI3K\/AKT and MAPK\/ERK pathways","volume":"8","author":"Liu","year":"2017","journal-title":"Oncotarget"},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Alkaabi, D., Arafat, K., Sulaiman, S., Al-Azawi, A.M., and Attoub, S. (2023). PD-1 Independent Role of PD-L1 in Triple-Negative Breast Cancer Progression. Int. J. Mol. Sci., 24.","DOI":"10.3390\/ijms24076420"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"397","DOI":"10.1038\/ncb1847","article-title":"Phosphorylation by Akt1 promotes cytoplasmic localization of Skp2 and impairs APCCdh1-mediated Skp2 destruction","volume":"11","author":"Gao","year":"2009","journal-title":"Nat. Cell Biol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"83","DOI":"10.1186\/s12943-017-0649-0","article-title":"Phosphorylation by mTORC1 stablizes Skp2 and regulates its oncogenic function in gastric cancer","volume":"16","author":"Geng","year":"2017","journal-title":"Mol. Cancer"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"605","DOI":"10.1016\/j.cell.2017.07.029","article-title":"The PI3K Pathway in Human Disease","volume":"170","author":"Fruman","year":"2017","journal-title":"Cell"},{"key":"ref_34","first-page":"3574","article-title":"Livin promotes the progression and metastasis of breast cancer through the regulation of epithelialmesenchymal transition via the p38\/GSK3beta pathway","volume":"38","author":"Han","year":"2017","journal-title":"Oncol. Rep."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1271","DOI":"10.1038\/sj.bjc.6604028","article-title":"Expression of inhibitor of apoptosis protein Livin in renal cell carcinoma and non-tumorous adult kidney","volume":"97","author":"Wagener","year":"2007","journal-title":"Br. J. Cancer"},{"key":"ref_36","unstructured":"Varki, A., Cummings, R., Esko, J., Freeze, H., Hart, G., and Marth, J. (2022). Chapter 27 S-type Lectins (Galectins). Essentials of Glycobiology, Cold Spring Harbor Laboratory Press. [4th ed.]."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"2463","DOI":"10.1016\/j.ejca.2014.06.015","article-title":"OTX008, a selective small-molecule inhibitor of galectin-1, downregulates cancer cell proliferation, invasion and tumour angiogenesis","volume":"50","author":"Riveiro","year":"2014","journal-title":"Eur. J. Cancer"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1758835918794622","DOI":"10.1177\/1758835918794622","article-title":"Upregulation of LGALS1 is associated with oral cancer metastasis","volume":"10","author":"Li","year":"2018","journal-title":"Ther. Adv. Med. Oncol."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"3137","DOI":"10.3892\/or.2017.5533","article-title":"Induction of galectin-1 by TLR-dependent PI3K activation enhances epithelial-mesenchymal transition of metastatic ovarian cancer cells","volume":"37","author":"Park","year":"2017","journal-title":"Oncol. Rep."},{"key":"ref_40","doi-asserted-by":"crossref","unstructured":"Zhang, Z., Richmond, A., and Yan, C. (2022). Immunomodulatory Properties of PI3K\/AKT\/mTOR and MAPK\/MEK\/ERK Inhibition Augment Response to Immune Checkpoint Blockade in Melanoma and Triple-Negative Breast Cancer. Int. J. Mol. Sci., 23.","DOI":"10.3390\/ijms23137353"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"eaao3810","DOI":"10.1126\/scisignal.aao3810","article-title":"Skp2-dependent reactivation of AKT drives resistance to PI3K inhibitors","volume":"11","author":"Clement","year":"2018","journal-title":"Sci. Signal."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"21138","DOI":"10.3390\/ijms160921138","article-title":"PI3K and AKT: Unfaithful Partners in Cancer","volume":"16","author":"Faes","year":"2015","journal-title":"Int. J. Mol. Sci."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"1729299","DOI":"10.1080\/2162402X.2020.1729299","article-title":"PD-L1 is overexpressed on breast cancer stem cells through notch3\/mTOR axis","volume":"9","author":"Mansour","year":"2020","journal-title":"Oncoimmunology"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"2799","DOI":"10.1002\/stem.2473","article-title":"Fascin Is Critical for the Maintenance of Breast Cancer Stem Cell Pool Predominantly via the Activation of the Notch Self-Renewal Pathway","volume":"34","author":"Barnawi","year":"2016","journal-title":"Stem Cells"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"760","DOI":"10.1128\/MCB.20.3.760-769.2000","article-title":"HuR regulates p21 mRNA stabilization by UV light","volume":"20","author":"Wang","year":"2000","journal-title":"Mol. Cell. Biol."}],"container-title":["International Journal of Molecular Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1422-0067\/27\/6\/2741\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,3,18]],"date-time":"2026-03-18T07:36:12Z","timestamp":1773819372000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1422-0067\/27\/6\/2741"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,3,17]]},"references-count":45,"journal-issue":{"issue":"6","published-online":{"date-parts":[[2026,3]]}},"alternative-id":["ijms27062741"],"URL":"https:\/\/doi.org\/10.3390\/ijms27062741","relation":{},"ISSN":["1422-0067"],"issn-type":[{"value":"1422-0067","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,3,17]]}}}