Regulation of HSF1-responsive gene expression by N-terminal truncated form of p73alpha.

DNp73 is a transactivation domain (TAD)-truncated form of p73. The ability of DNp73alpha to regulate gene expression was examined using reporter assays with luciferase gene constructs. Among various promoter-regulated reporter genes tested, heat shock factor (HSF)-responsive gene expression was selectively activated by DNp73alpha, but not by other p73-isoforms with TAD and DNp73beta. Deletion of TAD endowed p73alpha with the ability to activate HSF-responsive gene expression, but deletion of N-terminal proline-rich domain (PRD) rendered both DNp73alpha and the TAD-deleted p73alpha inactive. Considering the inability of DNp73beta, which is the C-terminus-truncated form of DNp73alpha, to function, these results indicate that both the PRD and C-terminus are necessary for DNp73alpha to be able to activate the HSF-dependent gene expression. In addition to the reporter gene expression, both DNp73alpha and TAD-deleted p73alpha activated the expression of an endogenous gene, hsp70, corresponding with an increase in the active form of HSF1. Taken together, these results demonstrate that TAD-truncated p73alpha can activate HSF-dependent gene expression via induction of active HSF1.