Galectin-3 phosphorylation is required for its anti-apoptotic function and cell cycle arrest.
Galectin-3, a beta-galactoside-binding protein, is implicated in cell growth, adhesion, differentiation, and tumor progression by interactions with its ligands. Recent studies have revealed that galectin-3 suppresses apoptosis and anoikis that contribute to cell survival during metastatic cascades. Previously, it has been shown that human galectin-3 undergoes post-translational signaling modification of Ser(6) phosphorylation that acts as an "on/off" switch for its sugar-binding capability. We questioned whether galectin-3 phosphorylation is required for its anti-apoptotic function. Serine to alanine (S6A) and serine to glutamic acid (S6E) mutations were produced at the casein kinase I phosphorylation site in galectin-3. The cDNAs were transfected into a breast carcinoma cell line BT-549 that innately expresses no galectin-3. Metabolic labeling revealed that only wild type galectin-3 undergoes phosphorylation in vivo. Expression of Ser(6) mutants of galectin-3 failed to protect cells from cisplatin-induced cell death and poly(ADP-ribose) polymerase from degradation when compared with wild type galectin-3. The non-phosphorylated galectin-3 mutants failed to protect cells from anoikis with G(1) arrest when cells were cultured in suspension. In response to a loss of cell-substrate interactions, only cells expressing wild type galectin-3 down-regulated cyclin A expression and up-regulated cyclin D(1) and cyclin-dependent kinase inhibitors, i.e. p21(WAF1/CIP1) and p27(KIP1) expression levels. These results demonstrate that galectin-3 phosphorylation regulates its anti-apoptotic signaling activity.
Yoshii
Tadashi
T
Tumor Progression and Metastasis Program, Karmanos Cancer Institute, Wayne State University, 110 E. Warren Ave., Detroit, MI 48201, USA.
Fukumori
Tomoharu
T
Honjo
Yuichiro
Y
Inohara
Hidenori
H
Kim
Hyeong-Reh Choi
HR
Raz
Avraham
A
D023102:Anoikis; D000943:Antigens, Differentiation / Q000378:metabolism*; D017209:Apoptosis; D001665:Binding Sites; D015153:Blotting, Western; D047388:Casein Kinases; D002453:Cell Cycle; D002460:Cell Line; D002470:Cell Survival; D002945:Cisplatin / Q000494:pharmacology; D019925:Cyclin A / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D015536:Down-Regulation; D037502:Galectin 3; D006801:Humans; D008024:Ligands; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
D000943:Antigens, Differentiation; C493956:CDKN1A protein, human; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D018076:DNA, Complementary; D037502:Galectin 3; D008024:Ligands; D019253:Proto-Oncogene Proteins c-bcl-2; D012694:Serine; D004247:DNA; D011494:Protein Kinases; D047388:Casein Kinases; D002945:Cisplatin