Satelli Arun, Rao Prema S, Gupta Prem K, Lockman Paul R, Srivenugopal Kalkunte S, Rao U Subrahmanyeswara
The Anticancer Resistance Group and the Cancer Biology Center, Department of Pharmaceutical Sciences, Texas Tech University Health Sciences Center, TX 79106, USA.
Oncol Rep. 2008 Mar;19(3):587-94.
Galectins play a key role in oncogenic processes. Although several galectins are known, their relative expression at the mRNA and protein levels, the subcellular localization, and their relationship to the oncogenic manifestation remains unclear. Herein we report a comprehensive characterization of the expression of major galectins in human breast cancer (drug-sensitive MCF-7 and drug-resistant MCF-7/Adr(R)), colon cancer (HCT-116 and HT-29), and glioma (T98G) cell lines, as these cells are common model systems for studying oncogenic processes. The expected approximately 14.5 kDa galectin-1, predominantly cytosolic, was detected in the cancer and normal cell lines. Notably, two different molecular forms of galectin-1 with molecular masses of approximately 13.5 and 15 kDa were detected in T98G cells, the latter being in the extracellular medium, perhaps a result of post-translational processing. Immunocytochemistry indicated that the extracellular galectin-1 bound to the cell surface was punctated in appearance, suggesting that it was bound to specific receptors. Immunohistological studies indicated that metastasizing carcinomas express high levels of galectin-1. On the other hand, galectin-3 was readily detectable in all cancer cell lines but undetectable in normal cell lines, indicating that galectin-3 is a cancer-specific biomarker protein. Galectin-3 was a cytosolic protein but was not detected in the extracellular medium, indicating that cancer cells do not secrete this galectin. Finally, despite the RT-PCR analysis suggesting the presence of two transcripts of galectin-8 in all cancer cell lines, the corresponding approximately 36 kDa protein was only detectable in the nuclear and cytosolic fractions upon cell fractionation. Notably, a different molecular form of galectin-8 of approximately 18 kDa was immunoprecipitated from the extracellular media, suggesting that the secreted galectin-8 undergoes post-translational processing. These results highlight the expression of galectins in different molecular forms in cancers, warranting caution in interpreting the results of functional studies of individual galectins, particularly because these proteins function redundantly in cancer pathways.
半乳糖凝集素在致癌过程中起关键作用。尽管已知几种半乳糖凝集素，但其在mRNA和蛋白质水平的相对表达、亚细胞定位以及它们与致癌表现的关系仍不清楚。在此，我们报告了人类乳腺癌（药物敏感的MCF-7和耐药的MCF-7/Adr(R)）、结肠癌（HCT-116和HT-29）以及胶质瘤（T98G）细胞系中主要半乳糖凝集素表达的全面特征，因为这些细胞是研究致癌过程的常用模型系统。预期约14.5 kDa的半乳糖凝集素-1主要存在于细胞质中，在癌细胞系和正常细胞系中均被检测到。值得注意的是，在T98G细胞中检测到两种不同分子量的半乳糖凝集素-1分子形式，分别约为13.5 kDa和15 kDa，后者存在于细胞外培养基中，这可能是翻译后加工的结果。免疫细胞化学表明，结合在细胞表面的细胞外半乳糖凝集素-1外观呈点状，表明它与特定受体结合。免疫组织学研究表明，转移性癌表达高水平的半乳糖凝集素-1。另一方面，半乳糖凝集素-3在所有癌细胞系中均易于检测到，但在正常细胞系中未检测到，这表明半乳糖凝集素-3是一种癌症特异性生物标志物蛋白。半乳糖凝集素-3是一种细胞质蛋白，但在细胞外培养基中未检测到，这表明癌细胞不分泌这种半乳糖凝集素。最后，尽管逆转录-聚合酶链反应（RT-PCR）分析表明所有癌细胞系中均存在半乳糖凝集素-8的两种转录本，但在细胞分级分离后，相应的约36 kDa蛋白仅在细胞核和细胞质组分中可检测到。值得注意的是，从细胞外培养基中免疫沉淀出一种约18 kDa的不同分子形式的半乳糖凝集素-8，这表明分泌的半乳糖凝集素-8经历了翻译后加工。这些结果突出了癌症中半乳糖凝集素以不同分子形式表达，这在解释单个半乳糖凝集素的功能研究结果时需要谨慎，特别是因为这些蛋白在癌症通路中具有冗余功能。
