Functional regulation of tyrosinase and LAMP gene family of melanogenesis and cell death in immortal murine melanocytes after repeated exposure to ultraviolet B

Abstract

This study characterizes the induction of melanogenesis and the expression of tyrosinase, tyrosinase-related protein (TRP) and lysosome-associated membrane protein (LAMP) gene families in the cultured melanocyte lines of non-agouti mice with four major genetic loci, i.e. melan-a2 (black, wild type), melan-b (brown, TRP-1 mutation), melan-s (black, piebaldism mutation) and melan-c (white, tyrosinase mutation) in response to repeated exposure to ultraviolet (UV) B (5 mJ/cm2, 7 consecutive days). Electron microscopy showed that new melanogenesis was induced in melan-a2, melan-s and melan-b melanocytes. Melan-a2, melan-s and melan-b showed an almost twofold increase in tyrosinase activity and gene expression with increased synthesis of melanosomes, although melan-b showed a minimum increase in tyrosinase activity. There was a twofold upregulation of LAMP-1 mRNA but no alteration in LAMP-2 and LAMP-3 mRNA expression in melan-a2, while there was no alteration in LAMP-1 mRNA expression but increased expression of LAMP-2 and LAMP-3 mRNA in melan-s, LAMP-3 showing a higher increase. Melan-b cells showed the same gene expression of LAMP-1, LAMP-2 and LAMP-3 as that of non-UV exposed cells. All three lines, however, exhibited simultaneously cell death, melan-b reaching the highest rate of cell death (96.5%). In contrast, melan-c, which did not have any tyrosinase activity with failure of melanogenesis induction, expressed all the mRNAs of the tyrosinase and LAMP gene families, but was not associated with any significant melanocyte death. Our study indicated: (i) that melanogenesis induction and melanocyte death are two photobiological processes occurring simultaneously after repeated UVB exposure, (ii) that in response to an upregulation of tyrosinase mRNA and enzymic activity, there was a co-ordinated upregulation of the LAMP-1 gene in wild type melan-a2, while no upregulation was found in melan-s and melan-b mutants, and (iii) that UV-induced melanocyte death is related to the upregulation of the tyrosinase gene, induction of new melanogenesis and mutation of the TRP-1 gene in immortal murine melanocytes.

Genetic and Epigenetic Control of the Proliferation and Differentiation of Mouse Epidermal Melanocytes in Culture

“…2A), which possess lattice-like internal structures. Similar observations have been reported on hair bulb melanocytes of brown (C57BR/cdJ) mice (Moyer, 1966), on choroidal melanocytes of brown (B6-blb) mice (Hearing et al, 19731, on regenerating hair bulb melanocytes of brown (BG-b/b ) mice (Prota et al, 1995), and on an immortal epidermal melanocyte line (melan-b; Bennett et al, 1989) derived from a brown (partially inbred Q strain) mouse (Ota et al, 1998). Although the reason why eumelanin synthesis is reduced in brown melanocytes, despite their higher tyrosinase activity, cannot be fully explained at present, it might be caused by the modification of tyrosinase activity, owing to the defect in the function of TRP-l/DHICA oxidase Kobayashi et al, 1994b) or to the defect in the stabilization of tyrosinase (Kobayashi et al, 1998).…”

“…In agouti melanocytes, the proportion of stage IV melanosomes in the total number of melanosomes is lower than that in black melanocytes. N, nucleus; M, mitochondria; Hirobe et al, 1998Hirobe et al, 1998Hirobe et al, 1998Ota et al, 1998Abe et al, 1986 d (D Halaban et al, 1988 ? Bennett et al, 1989 0 1 E g Hirobe et al, 1998Wu et al, 1997Hirobe et al, 1998Sviderskaya et al, 1997 2 .…”

Syntaxin 7 Complexes with Mouse Vps10p Tail Interactor 1b, Syntaxin 6, Vesicle-associated Membrane Protein (VAMP)8, and VAMP7 in B16 Melanoma Cells

“…As such, melanosomes are likely to be derivatives of the late endosomal pathway. Previously it has been found that the induction of melanogenesis results in the coordinate expression of tyrosinase and lysosome-associated membrane protein 1 (29), implying that these proteins are expressed as part of a developmental program that facilitates the biogenesis of melanosomes. Consistent with this idea we have found that expression of Syntaxin 7 is also induced during melanogenesis in B16 cells (Fig.…”

Neprilysin, a Novel Target for Ultraviolet B Regulation of Melanogenesis Via Melanocortins

“…UVB has already been described to regulate protein expression in melanocytes, especially enzymes directly involved in melanogenesis, such as tyrosinase, TRP1, and TRP2 (Friedmann and Gilchrest, 1987;Ramirez-Bosca et al, 1992;Aberdam et al, 1993), but also lysosome-associated membrane proteins (Ota et al, 1998) and anti-oxidant enzymes such as catalase (Bessou-Touya et al, 1998); however, this is to our knowledge one of the ®rst demonstrations of an inhibitory effect of UVB on a melanocyte protease. Noteworthy, downregulation by UVB does not seem to be a general feature of melanocyte surface peptidases as the activity of dipeptidyl peptidase IV was not found to be modi®ed by UVB treatment (data not shown).…”