Gordon, S. J. V. | bioRxiv Science

bioRxiv2019

MTF1, a classic metal sensing transcription factor, promotes myogenesis in response to copper.

MTF1 is a conserved metal-binding transcription factor in eukaryotes that binds to conserved DNA sequence motifs, termed metal response elements (MREs). MTF1 responds to metal excess and deprivation, protects cells from oxidative and hypoxic stresses, and is required for embryonic development in vertebrates. We used multiple strategies to identify an unappreciated role for MTF1 and copper (Cu) in cell differentiation. Upon initiation of myogenesis from primary myoblasts, MTF1 expression increased, as did nuclear localization. Mtf1 knockdown impaired differentiation, while addition of non-toxic concentrations of Cu+ enhanced MTF1 expression and promoted myogenesis. Cu+ bound stoichiometrically to a C-terminus tetra-cysteine of MTF1. MTF1 bound to chromatin at the promoter regions of myogenic genes and binding was stimulated by copper. MTF1 formed a complex with MyoD at myogenic promoters, the master transcriptional regulator of the myogenic lineage. These studies establish novel mechanisms by which copper and MTF1 regulate gene expression in myoblast differentiation.

cell biology↗

bioRxiv2018

Manganese influx and expression of ZIP8 is essential in primary myoblasts and contributes to activation of SOD2

Trace elements such as copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn) are enzyme cofactors and second messengers in cell signaling. Trace elements are emerging as key regulators of differentiation and development of mammalian tissues including blood, brain, and skeletal muscle. We previously reported an influx of Cu and dynamic expression of various metal transporters during differentiation of skeletal muscle cells. Here, we demonstrate that during differentiation of skeletal myoblasts an increase of additional trace elements such as Mn, Fe and Zn occurs. Interestingly the Mn increase is concomitant with increased Mn-dependent SOD2 levels. To better understand the Mn import pathway in skeletal muscle cells, we probed the functional relevance of the closely related proteins ZIP8 and ZIP14, which are implicated in Zn, Mn, and Fe transport. Partial depletion of ZIP8 severely impaired growth of myoblasts and led to cell death under differentiation conditions, indicating that ZIP8-mediated metal transport is essential in skeletal muscle cells. Moreover, knockdown of Zip8 impaired activity of the Mn-dependent SOD2. Growth defects were partially rescued by Mn supplementation to the medium, suggesting additional functions for ZIP8 in the skeletal muscle lineage. Knockdown of Zip14, on the other hand, had only a mild effect on myotube size, consistent with a role for ZIP14 in muscle hypertrophy. This is the first report on the functional relevance of two members of the ZIP family of metal transporters in the skeletal muscle lineage, and further supports the paradigm that trace metal transporters are critical modulators of mammalian tissue development.

cell biology↗