Biology subjects

White, J. H.

Publications and source records attributed to White, J. H..

2 recordsLinked to original sources

bioRxiv2020

Vitamin D regulates MerTK-dependent phagocytosis in human myeloid cells

Vitamin D deficiency is a major environmental risk factor for the development of multiple sclerosis (MS). The major circulating metabolite of vitamin D (25OHD) is converted to the active form (calcitriol) by the hydroxylase enzyme CYP27B1. In MS lesions the tyrosine kinase MerTK expressed by microglia and macrophages regulates phagocytosis of myelin debris and apoptotic cells that can accumulate and inhibit tissue repair and remyelination. We show that calcitriol downregulates MerTK mRNA and protein expression in adult human microglia and monocyte-derived macrophages, thereby inhibiting myelin phagocytosis and apoptotic cell clearance. Proinflammatory myeloid cells express high levels of CYP27B1 compared to homeostatic (TGF{beta}-treated) myeloid cells. Only proinflammatory cells in the presence of TNF- generate calcitriol from 25OHD, resulting in repression of MerTK expression and function. The selective production of calcitriol in proinflammatory myeloid cells leading to downregulation of MerTK-mediated phagocytosis has the potential to reduce the risk for auto-antigen presentation while retaining the phagocytic ability of homeostatic myeloid cells, thereby contributing to inflammation reduction and enhanced tissue repair.

immunology↗

bioRxiv2018

The tumor suppressor FBW7 and the vitamin D receptor are mutual cofactors.

The E3 ligase FBW7 targets drivers of cell cycle progression such as c-MYC for proteasomal degradation. It is frequently mutated in cancer, and is a tumor suppressor. Extensive epidemiological data links vitamin D deficiency to increased incidence of several cancers, although the underlying cancer-preventive mechanisms are poorly understood. Here, we show that hormonal 1,25-dihydroxyvitamin D3 (1,25D) rapidly stimulates the interaction of the VDR with FBW7, and that of FBW7 with c-MYC. In contrast, it blocks the association of FBW7 with c-MYC antagonist MXD1. 1,25D also enhances the association of FBW7, proteasome subunits, and ubiquitin with DNA-bound c-MYC, consistent with induced degradation of c-MYC on DNA. In addition to c-MYC, 1,25D accelerates the turnover of other FBW7 target proteins. Intriguingly, FBW7 is essential for optimal VDR gene expression. It is also recruited to VDR targets genes, and its depletion attenuates 1,25D-stimulated VDR DNA binding, transactivation, and cell cycle arrest. Thus, the VDR and FBW7 are mutual cofactors, which provides a molecular basis for the cancer-preventive actions of vitamin D through accelerated turnover of FBW7 target proteins.

molecular biology↗