Proteins of the Homeodomain-Interacting Protein Kinase (HIPK) family are nuclear serine/threonine kinases that phosphorylate a variety of targets including numerous transcription factors. The functions of the mammalian members of this protein family (HIPK1-4) include roles in development and in regulation of cellular proliferation. These proteins also modulate cellular responses to various stress stimuli including DNA damage and hypoxia. We are using Caenorhabditis elegans to study HIPK function by examining the sole nematode member of this protein family, HPK-1.

We have found that levels of HPK-1 are regulated by heat stress, and that HPK-1 contributes to survival following heat or oxidative stress. Additionally, we have shown that HPK-1 is required for normal longevity, with loss of HPK-1 function leading to a faster decline of physiological processes that reflect premature ageing. Through microarray analysis, we have found that HPK-1-regulated genes include those encoding proteins that serve important functions in stress responses such as Phase I and Phase II detoxification enzymes. Consistent with a role in longevity assurance, HPK-1 also regulates the expression of age-regulated genes.

To discover the mechanisms by which HPK-1 functions we performed a nuclear phosphoproteomic analysis. We used iTRAQ quantitative mass spectrometry to identify potential HPK-1 phosphorylation targets. Among the proteins that are phosphorylated in a HPK-1-dependent manner are transcription factors with roles in development and in regulating stress responses and ageing.

Our work in C. elegans has provided the first evidence of a role for a metazoan member of the HPK-1 protein family in the response to heat stress and is providing mechanistic insight into the roles of this kinase family in both development and ageing.