Role of HSPB1 phosphorylation on PTEN and proteins related to breast cancer progression: Preliminary results.

GISELA N CASTRO, NIUBYS CAYADO-GUTIÉRREZ, FELIPE CARLOS MARTIN ZOPPINO, MARIEL A. FANELLI F., DARÍO CUELLO-CARRIÓN, DANIEL R. CIOCCA

Workshop; First Conference of the South American Chapter of Cell Stress Society International; 2014

We recently reported a novel function of HSPB1 (HSP27) modulating phosphatase and tensin homologue (PTEN) levels in human breast cancer cells. We suggested that HSPB1 interacts with PTEN decreasing its stability. HSPB1 form heterogenous oligomers in a dynamic equilibrium regulated by its phosphorylation, it is unknown the role of HSPB1 phosphorylation in PTEN regulation and the implications for other proteins involved in breast cancer progression. Here we have examined the role of HSPB1 phosporylation on PTEN levels and its relation to proteins associated to tumor progression: β-catenin, caveolin-1, NHERF1 and HER2/neu. MCF-7 cells were transfected with two HSPB1 mutants in which the phosphorylatable serine residues have been replaced by: a) aspartate to mimic the phosphorylated protein or b) alanine to mimic the non-phosphorylated protein. The proteins were evaluated by immunocytochemistry, immunofluorescence and immunoblotting. We found that endogenous HSPB1 phosphorylation was not affected in the aspartate mutant however a 1.5 fold increased in HSPB1 levels was observed (suggesting that the mutant is working). This mutant showed a slight overall increase of PTEN levels. Surprisingly a significant raise in p-PTEN levels (inactive form) was found, suggesting that p-HSPB1 could be involved in PTEN degradation. A highly significant increase in β-catenin was note in the aspartate mutant suggesting that p-HSPB1 is strongly related to β-catenin up-regulation and in addition, this protein was translocated to the nuclei. HER2/neu was significantly up-regulated, while NHERF1 showed no significant changes. Finally, a significant reduction in Cav-1 levels was found in the aspartate mutant and also in the alanine mutant. In conclusion, HSPB1 phosphorylation modulates PTEN inactive form as wells as proteins associated to tumor progression.