Protein Kinase D1 Has a Key Role in Wound Healing and Skin Carcinogenesis

Abstract

Protein kinase D (PKD) is a family of stress-responsive serine/threonine kinases implicated in the regulation of diverse cellular functions including cell growth, differentiation, apoptosis, and cell motility. Although all three isoforms are expressed in keratinocytes, their role in skin biology and pathology is poorly understood. We recently identified a critical role for PKD1 during reversal of keratinocyte differentiation in culture, suggesting a potential pro-proliferative role in epidermal adaptive responses. Here, we generated mice with targeted deletion of PKD1 in epidermis to evaluate the significance of PKD1 in normal and hyperplastic conditions. These mice displayed a normal skin phenotype indicating that PKD1 is dispensable for skin development and homeostasis. Upon wounding however, PKD1-deficient mice exhibited delayed wound re-epithelialization correlated with a reduced proliferation and migration of keratinocytes at the wound edge. In addition, the hyperplastic and inflammatory responses to topical phorbol ester were significantly suppressed suggesting involvement of PKD1 in tumor promotion. Consistently, when subjected to two-stage chemical skin carcinogenesis protocol, PKD1-deficient mice were resistant to papilloma formation when compared to control littermates. These results revealed a critical pro-proliferative role for PKD1 in epidermal adaptive responses, suggesting a potential therapeutic target in skin wound and cancer treatment.

Opposing Growth Regulatory Roles of Protein Kinase D Isoforms in Human Keratinocytes

“…Our own genetic in vitro and in vivo studies in mouse skin did not support a role for PKD1 in epidermal homeostasis. These studies however, revealed a critical and unique pro-proliferative role for PKD1 signaling in epidermal adaptive responses including stressinduced de-differentiation, wound re-epithelialization, and tumor promotion and development (14,15). Interestingly, despite expression of all PKD isoforms in mouse KCs, PKD2, and PKD3 could not fully compensate for the loss of PKD1 signaling in stress-induced responses of mouse KCs.…”

“…1C). Given that transcripts of all PKD isoforms are detected in mouse KCs (14), transcript levels of PKD isoforms in total RNA isolated from mouse and human KCs were analyzed by RT-qPCR. As expected all three PKD isoforms were expressed in mouse KCs, albeit at variable levels ( Fig.…”

Distinct Functions of Epidermal and Myeloid-Derived VEGF-A in Skin Tumorigenesis Mediated by HPV8

“…7B). In epidermal tissue, transcripts for VEGFR1 or VEGFR2 were hardly detectable in both UV-treated and untreated skin of the 3 mouse strains and we are reluctant to draw any conclusion on these findings with regards to expression of VEGFRs (DC t values for qRT-PCR analysis were in the range of [29][30][31][32][33][34]. Therefore, to further refine the analysis of VEGF receptor expression in keratinocytes and to exclude contamination of epidermal tissue with dermal cells, Epcam…”

“…For investigation of the average blood vessel density, staining for CD31 and VEGFR2 was quantified in six representative highpower fields (HPF, 200 Â 300 mm 2 )/section in at least two independent sections of one lesion using ImageJ software; the data are expressed as the percentage of CD31 or VEGFR2-positive areas within the dermal tumor stroma. Ki-67-positive keratinocytes were quantified as described previously (34,35). Briefly, Ki-67-positive cells were determined within the stratum basale of lesional skin over a distance of 100 mm in five representative fields/section in at least two independent sections of one lesion; the data are expressed as the percentage of Ki-67-positive basal cells.…”

Regenerative Medicine: Charting a New Course in Wound Healing

“…For example, protein kinase D1 has been found to play a critical role in the reversal of keratinocyte differentiation in culture, and deletion of this enzyme in mice led to delayed wound reepithelialization that correlated with decreased proliferation and migration of keratinocytes at the wound edge. 95 Gap junction proteins such as connexin-43 are also being targeted with synthetic peptides 96 and antisense oligonucleotides. 97 Overall, it is possible that the targeting of individual proteins, genes, or even pathways (irrespective of the approach used) will be insufficient to effect regeneration.…”