Human epidermal keratinocytes (KCs), especially those in hyperproliferative diseases, synthesize and respond to a large number of bio-active fatty acid derivatives such as prostaglandins (PGs) and hydroxyeicosatetraenoic acids (HETEs). These compounds activate nuclear or plasma membrane receptors. Peroxisome proliferator (PP) activated receptor (PPARs) are members of the nuclear receptor (NR) super family of ligand-activated transcription factors and play critical roles in tissue specialization and cell differentiation. PGs and HETEs are suspected to be endogenous ligands for PPARs. The relatively high effective concentrations needed for these compounds' effects suggests they may be serving as the precursor compound for the active metabolite or are subjected to rapid degradation. We, and others have shown PPAR activation in KCs is accompanied by a striking increase in specific and overall markers of terminal differentiation. In a new avenue of studies, our current preliminary data and analysis of the literature suggest an innovative means for PG and HETE synthetic enzymes to regulate PPAR in addition to ligand (PG and HETE) synthesis. Our central hypothesis is that certain enzymes producing bio-active fatty acid derivatives may serve a dual function as NR regulatory proteins through their physical interaction with the receptor thus providing a local source or possible higher concentration of the often short-lived receptor ligand. To date, no analysis of NR co-regulatory proteins has been reported for epidermal KCs much less in regard to a NR such as PPAR apparently so potently able to influence epidermal differentiation further adding to the novel nature of this work.
The Specific Aims for this high-risk R21 study will focus on establishing """"""""proof of concept"""""""" for direct interaction of PPAR with the synthetic enzymes through in vitro protein-protein interaction studies, yeast and mammalian two-hybrid analyses and regulation of PPAR-dependent reporter genes. Future work could address the enzyme's association with additional transcription complex factors through other inherent interaction motifs. PPs, PPARs and possibly enzymes of the fatty acid derivative cascade in their novel role as PPAR co-regulatory proteins could offer distinct but complimentary avenues for clinically manipulating the ability of PPAR to regulate KC growth and differentiation relevant to improving barrier regeneration in cutaneous wounds or quelling hyperplastic skin diseases.
