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Vitiligo, a common skin disorder, is characterized by the loss of functional melanocytes resulting in the depigmentation of skin. Previous studies have demonstrated molecular and architectural alterations in the epidermal keratinocytes upon loss of melanocytes. The physiological implications of these "altered" keratinocytes are yet not known. We investigated the wound healing efficiency of lesional vs nonlesional skin in 12 subjects with stable nonsegmental vitiligo using histological and ultrastructural evaluation of partial‐thickness wounds. The wounds were examined 12 days postinjury, coinciding with the reepithelialization phase of healing marked primarily by keratinocyte migration and proliferation. This study demonstrated a significant difference in the reepithelialization potential between the lesional and nonlesional skin. While all 12 nonlesional wounds demonstrated considerable neoepidermis formation on the 12th day post wound, only four of the corresponding lesional samples showed comparable reepithelialization; the rest remaining in the inflammatory phase. Ultrastructural studies using transmission electron microscopy as well as immunohistochemical staining revealed a reduced number of desmosomes, shorter keratin tonofilaments and an increase in myofibroblast population in the dermis of lesional reepithelialized tissue compared to the nonlesional reepithelialized samples. This study implicates gross functional perturbations in the lesional skin during physiological wound healing in vitiligo, suggesting that the breakdown of keratinocyte‐melanocyte network results in delayed wound repair kinetics in the lesional skin when compared to patient‐matched nonlesional skin. [ABSTRACT FROM AUTHOR]

Endoplasmic reticulum (ER)-plasma membrane (PM) junctions form functionally active microdomains that connect intracellular and extracellular environments. While the key role of these interfaces in maintenance of intracellular Ca2+ levels has been uncovered in recent years, the functional significance of ER-PM junctions in nonexcitable cells has remained unclear. Here, we show that the ER calcium sensor protein STIM1 (stromal interaction molecule 1) interacts with the plasma membrane-localized adenylyl cyclase 6 (ADCY6) to govern melanogenesis. The physiological stimulus a-melanocytestimulating hormone (αMSH) depletes ER Ca2+ stores, thus recruiting STIM1 to ER-PM junctions, which in turn activates ADCY6. Using zebrafish as a model system, we further established STIM1's significance in regulating pigmentation in vivo. STIM1 domain deletion studies reveal the importance of Ser/Pro-rich C-terminal region in this interaction. This mechanism of cAMP generation creates a positive feedback loop, controlling the output of the classical αMSHcAMP- MITF axis in melanocytes. Our study thus delineates a signaling module that couples two fundamental secondary messengers to drive pigmentation. Given the central role of calcium and cAMP signaling pathways, this module may be operative during various other physiological processes and pathological conditions. [ABSTRACT FROM AUTHOR]

Vitiligo is a multifactorial acquired depigmenting disorder. Recent insights into the molecular mechanisms driving the gradual destruction of melanocytes in vitiligo will likely lead to the discovery of novel therapies, which need to be evaluated in animal models that closely recapitulate the pathogenesis of human vitiligo. In humans, vitiligo is characterized by a spontaneous loss of functional melanocytes from the epidermis, but most animal models of vitiligo are either inducible or genetically programmed. Here, we report that acquired depigmentation in water buffalo recapitulates molecular, histological, immunohistochemical, and ultrastructural changes observed in human vitiligo and hence could be used as a model to study vitiligo pathogenesis and facilitate the discovery and evaluation of therapeutic interventions for vitiligo. [ABSTRACT FROM AUTHOR]

The putative proteasome-associated proteins Mpa (Mycobaterium proteasomal ATPase) and PafA (proteasome accessory factor A) of the human pathogen Mycobacterium tuberculosis (Mtb) are essential for virulence and resistance to nitric oxide. However, a direct link between the proteasome protease and Mpa or PafA has never been demonstrated. Furthermore, protein degradation by bacterial proteasomes in vitro has not been accomplished, possibly due to the failure to find natural degradation substrates or other necessary proteasome co-factors. In this work, we identify the first bacterial proteasome substrates, malonyl Co-A acyl carrier protein transacylase and ketopantoate hydroxymethyltransferase, enzymes that are required for the biosynthesis of fatty acids and polyketides that are essential for the pathogenesis of Mtb. Maintenance of the physiological levels of these enzymes required Mpa and PafA in addition to proteasome protease activity. Mpa levels were also regulated in a proteasome-dependent manner. Finally, we found that a conserved tyrosine of Mpa was essential for function. Thus, these results suggest that Mpa, PafA, and the Mtb proteasome degrade bacterial proteins that are important for virulence in mice. [ABSTRACT FROM AUTHOR]

Tanning response and melanocyte differentiation are mediated by the central transcription factor MITF. This involves the rapid and selective induction of melanocyte maturation genes, while concomitantly the expression of other effector genes is maintained. In this study, using cell‐based and zebrafish model systems, we report on a pH‐mediated feed‐forward mechanism of epigenetic regulation that enables selective amplification of the melanocyte maturation program. We demonstrate that MITF activation directly elevates the expression of the enzyme carbonic anhydrase 14 (CA14). Nuclear localization of CA14 leads to an increase of the intracellular pH, resulting in the activation of the histone acetyl transferase p300/CBP. In turn, enhanced H3K27 histone acetylation at selected differentiation genes facilitates their amplified expression via MITF. CRISPR‐mediated targeted missense mutation of CA14 in zebrafish results in the formation of immature acidic melanocytes with decreased pigmentation, establishing a central role for this mechanism during melanocyte differentiation in vivo. Thus, we describe an epigenetic control system via pH modulation that reinforces cell fate determination by altering chromatin dynamics. Synopsis: Melanocyte differentiation is mediated by the transcription factor MITF. A feed‐forward loop involving MITF and the carbonic anhydrase 14 enables the rapid and selective expression of pigmentation genes via pH‐dependent epigenetic marks. The expression of carbonic anhydrase 14 (CA14) is positively regulated by the transcription factor MITF.Nuclear localization of CA14 elevates intracellular pH, which activates p300 and increases H3K27ac at MITF targets.Increased H3K27 acetylation promotes the expression of MITF‐dependent pigmentation genes. [ABSTRACT FROM AUTHOR]

FadD28 from Mycobacterium tuberculosis belongs to the fatty-acyl AMP ligase (FAAL) family of proteins. It is essential for the biosynthesis of a virulent phthiocerol dimycocerosate (PDIM) lipid that is only found in the cell wall of pathogenic mycobacteria. The N-terminal domain, comprising of the first 460 residues, was crystallized by the hanging-drop vapour-diffusion method at 295 K. The crystals belong to space group P212121, with unit-cell parameters a = 50.97, b = 60.74, c = 136.54 Å. The crystal structure of the N-terminal domain of FadD28 at 2.35 Å resolution has been solved using the MAD method. [ABSTRACT FROM AUTHOR]

The biosynthetic machinery of polyketide synthases involves various sequential enzymatic reactions, such as initiation, elongation and cyclization, to produce polyketides. PKS18 protein from Mycobacterium tuberculosis belongs to the type III polyketide synthase family and displays an unusual starter-unit specificity to catalyze the formation of α-pyrones. This enzyme uses malonyl-CoA to iteratively extend long-chain aliphatic coenzyme A (C12 to C20) molecules, producing triketide and tetraketide pyrone products. In order to aid in understanding the structural basis of this long-chain specificity and to further characterize the enzymatic mechanism of PKS18, the protein has been crystallized. The crystal belongs to the triclinic space group P1, with unit-cell parameters a = 59.9, b = 80.7, c = 99.6 Å, α = 108.2, β = 93.0, γ = 103.7 °. [ABSTRACT FROM AUTHOR]