HSPA1A and myeloproliferative disorder: Additionally, HSP70 modulates proliferative pathways via MAPK; it modulates JNK and, RAF-1 and ERK phosphorylation [18-20] HSP70 and HSP90 share the ability to inhibit APAF-1 to block the apoptosis cascade, [21] and it is tempting to speculate a major role of HSP70 and HSP90 in the apoptotic resistance of MPN.