Cathelicidin antimicrobial peptide (CAMP) is a key antimicrobial peptide in skin. CAMP production is increased during epidermal differentiation and enriched in the stratum corneum. We recently identified a novel endoplasmic reticulum (ER) stress-mediated sphingosine-1-phosphate (S1P)-dependent mechanism of CAMP synthesis. In this study, we found that S1P synthesized by an isoform of sphingosine kinase (SPHK), SPHK1, serves as a signal for CAMP synthesis; and conversely, another isoform SPHK2 likely has a suppressor or no role in CAMP synthesis. Pertinently, prior studies showed that physiological ER stress is essential for normal epidermal differentiation. We here show that: increased ER stress occurs in differentiated cultured keratinocytes (KC); 2) increases in both CAMP and S1P production depend upon differentiation level of KC (proliferated
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