mTORC2-PKBα/Akt1 Serine 473 Phosphorylation Axis Is Essential for Regulation of FOXP3 Stability by Chemokine CCL3 in Psoriasis

The connection between infections and acute guttate psoriasis (AGP) outbreaks/chronic plaque psoriasis (CPP) exacerbation has been known for years. Impaired function of FOXP3 + Tregs in psoriasis has been identified. However, the mechanisms behind these two observations have not been fully interpreted. In the present study, we provide evidence to support chemokine CCL3 as one of the vital links between infections and FOXP3 stability in the psoriatic microenvironment. We found that serum CCL3, strongly induced by microorganism infections including streptococcus, was closely correlated with FOXP3 levels in CD4 + CD25 + T cells of patients with psoriasis. CCL3 manipulated FOXP3 stability in a concentration-dependent bidirectional manner. High-concentration CCL3 decreased FOXP3 stability by promoting FOXP3's degradation through K48-linkage ubiquitination. This degradation was mainly dependent on upregulation of Serine 473 phosphorylation of the PKB alpha/Akt1 isoform, and almost independent of mTORC1 (mammalian target of rapamycin complex 1) activity. On the other hand, low-concentration CCL3 could enhance FOXP3 stability by the maintenance of the PKC pathway and the restriction of the PKB/Akt pathway. We further demonstrated that enhancing FOXP3 stability by low-concentration CCL3 attributed, at least partly, to the prevention of cytoplasmic Sin1, a vital component of mTORC2, nuclear translocation. Our results suggest vital roles for CCL3-mTORC2-isoform PKB/Akt1 S473 phosphorylation axis in FOXP3 + Tregs and the development of psoriasis. Journal of Investigative Dermatology (2013) 133, 418-428; doi:10.1038/jid.2012.333; published online 6 December 2012