Proteins of the Homeodomain-Interacting Protein Kinase (HIPK) family regulate an array of processes in mammalian systems, such as the DNA damage response and cellular proliferation. Members of this protein family are serine/threonine kinases that are predominantly localised to the nucleus. Caenorhabditis elegans expresses a single HIPK protein, called HPK-1. The HPK-1 protein is expressed in many cell types in the nematode and, like its mammalian counterparts, is localised to nuclear speckles, suggesting that it may be involved in analogous cellular processes. Previous studies have implicated HPK-1 in longevity control and we have recently suggested that this protein may be regulated in a stress-dependent manner as animals carrying a fosmid-based fluorescent reporter exhibit increased levels of HPK-1 following heat stress. To expand these observations, we have been investigating the role of HPK-1 in various processes, such as development, longevity, and in the response to stress, by conducting phenotypic analyses on a worm strain carrying a deletion mutation within the
hpk-1 gene. HPK-1 appears to be required for normal somatic and germline development, as animals lacking HPK-1 are reduced in size compared with their wildtype counterparts, and show a decrease in brood size. We have previously 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. Loss of HPK-1 function also renders worms hypersensitive to heat and oxidative stress, suggesting that HPK-1 contributes to survival following exposure to these stressors. In order to investigate the mechanisms involved in these processes, a nuclear phosphoproteomic study is underway to identify potential HPK-1 phosphorylation targets. Putative nuclear targets such as transcription factors for developmental, ageing and stress response pathways have been identified using Isobaric tags for relative and absolute quantitation (iTRAQ) labelling and tandem mass spectrometry, and these are currently being tested for functional associations with HPK-1.