The involvement of heat shock protein 27 in normal and cancer cell migration

Heat shock protein 27 [HSP27] belongs to the family of small heat shock proteins [sHSP] characterized by low molecular weight [15-42 kDa], formation of oligomeric structures and a conserved amino acid sequence known as the a-crystallin domain. HSP27 is normally expressed in various tissues [including breast, uterus, cervix, placenta, muscle, skin, heart] as well as in assorted human tumor cells. The expression of HSP27 varies during development, cell cycle, and cell differentiation and its phosphorylation at different serine residues modifies its quaternary structure and affects its function. Furthermore, it is established that microenvironmental factors as well as cell growth and differentiation alter HSP27 phosphorylation state, intracellular distribution and structural organization. HSP27 has several important functions including chaperoning activity [facilitating the refolding of partially denatured proteins], cell protection from apoptotic events, and facilitation of protein degradation by the proteasome machinery. In the last few years it is becoming increasingly clear that HSP27 also modulates cell migration. Cell migration is crucial for multiple biological processes such as angiogenesis, inflammation, wound healing, placental implantation, tumor progression and metastasis. Indeed, studies confirmed that HSP27 regulates normal cell migration [smooth muscle cells, vascular endothelial cells, fibroblasts, neutrophils and extravillous trophoblast cells during placental implantation]. Moreover, its involvement in cancer cell lines motility was demonstrated [glioblastoma, breast, melanoma, cervical and colon] and proteomic-based strategies demonstrated upregulation of HSP27 in several metastatic cancer cells [breast, colorectal and hepatocellular carcinomas]. HSP27 regulates cell motility by modulating F-actin polymerization and actin cytoskeleton organization. Moreover, several studies demonstrated that HSP27 function contributes to the activation of proteolytic enzymes which manipulate extracellular matrix [ECM] and thus cell invasiveness. Increased interest in HSP27 is already evidenced in exponentially mounting numbers of scientific reports published in the past months. It is also increasingly perceived that HSP27 may present an appropriate candidate for targeted therapy in cancer and metastasis. The present chapter summarizes the accumulated data regarding the role of HSP27 in cell migration and related signaling cascades and discusses their implications on cancer metastasis.