Contrast functions of αA- and αB-crystallins in cancer development

alpha-Crystallins, initially identified as the structural proteins of the ocular lens, belong to the small heat shock protein family. They play significant roles in maintaining the lens transparency and preventing protein aggregation. alpha-Crystallins exist in two isoforms: alpha A and alpha B, and they display differential tissue distribution. Their mutations are implicated in several human diseases including cardiac myopathies, neurodegenerative diseases, cataracts and various types of cancers. Increased alpha B expression was detected in retinoblastoma, breast cancer, glioblastoma, prostate and renal cell carcinomas, indicating its role in promoting tumor growth. A complex picture emerges for alpha A. Although earlier studies suggest that alpha A may promote cancer development, recent studies from our laboratory demonstrate that alpha A can act as a tumor suppressor inhibiting cell transformation and retarding cell migration through modulating MAP kinase activity. In this review, we summarize the recent progress about the functions of alpha A and alpha B in cancer development.