Growth factor signaling in keratinocytes is regulated by FIH-1: implication for wound healing

Epidermal growth factor receptor (EGFR) signaling has been shown to play a central role in keratinocyte migration and skin wound healing. Following its phosphorylation and activation, EGFR is rapidly internalized and transported in endosomes that is an endocytic membrane transport system, resulting in a degradation of activated EGFR. Therefore, manipulation of this trafficking induces the accumulation of activated EGFR in endosomes and prolongs activation of EGFR signaling. Recently, a protein kinase LRRK1 has been recognized as one of the regulators of EGFR endosomal trafficking. We were intrigued by LRRK1 since (i) depletion of LRRK1 inhibits the EGFR transport in endosomes, leading to stabilization of activated EGFR; and (ii) LRRK1 is a likely substrate of factor-inhibiting hypoxia-inducible factor 1 (FIH-1). FIH-1 hydroxylates proteins containing the ankyrin repeat domain (ARD) such as Notch, resulting in an inhibition of Notch activity. Since our preliminary data show that FIH-1: (i) enhances cell migration via upregulation of the EGFR; and (ii) interacts with LRRK1, we hypothesize that: the interaction of FIH-1 with LRRK1 sustains EGFR signaling by altering LRRK1-mediated EGFR endocytic trafficking resulting in enhanced keratinocyte migration. To test this hypothesis, we propose to investigate whether ectopic expression or knockdown of FIH-1 will: (i) alter the LRRK1/EGFR/Grb2 interaction in a hydroxylase -dependent manner; and (ii) affect the EGFR transport in endosomes. Additionally, we will investigate whether overexpression of LRRK1 will rescue FIH-1-induced: (i) impaired EGFR transport; (ii) increased EGFR activation; and (iii) enhanced wound sealing. Information garnered from this proposal will greatly enhance our understanding of how EGFR signaling can be modulated. Establishment of a FIH-1/LRRK1 relationship and its physiological significance is extremely novel as such an interaction in keratinocytes has heretofore not been considered. The most immediate clinical impact of these studies will be the development of innovative therapies for wound repair. For example, if LRRK1 negatively regulates keratinocyte migration, development of small molecule inhibitors of this kinase could be used as adjuvant therapy to enhance wound healing. Likewise, nanoparticle delivery of FIH-1 to keratinocytes should have great utility promoting migration in chronic wound situations. Finally, EGFR signaling plays a central role not only in keratinocyte migration, but also proliferation and differentiation, thus development of FIH-1 inhibitors and/or LRRK1-overexpression-based therapies could have potential utility in diseases such as psoriasis, atopic dermatitis and squamous cell carcinoma.