The C-Box Region of MAF1 Regulates Transcriptional Activity and Protein Stability

Abstract

MAF1 is a conserved negative regulator of RNA polymerase (pol) III and intracellular lipid homeostasis across species. Here, we show that the MAF1 C-box region negatively regulates its activity. Mutations in Caenorhabditis elegans mafr-1 that truncate the C-box retain the ability to inhibit the transcription of RNA pol III targets, reduce lipid biogenesis, and lower reproductive output. In human cells, C-box deletion of MAF1 leads to increased MAF1 nuclear localization and enhanced repression of ACC1 and FASN, but with impaired repression of RNA pol III targets. Surprisingly, C-box mutations render MAF1 insensitive to rapamycin, further defining a regulatory role for this region. Two MAF1 species, MAF1L and MAF1S, are regulated by the C-box YSY motif, which, when mutated, alters species stoichiometry and proteasome-dependent turnover of nuclear MAF1. Our results reveal a role for the C-box region as a critical determinant of MAF1 stability, activity, and response to cellular stress.

Roles for the RNA polymerase III regulator MAFR-1 in regulating sperm quality inCaenorhabditis elegans

“…Similarly, mafr-1 (KO) animals displayed increased intracellular lipid abundance relative to age-matched WT control animals ( Fig. 1E), as expected from previous studies (Khanna et al, 2014;Mierzejewska and Chreptowicz, 2016;Palian et al, 2014;Pradhan et al, 2017). Our previous investigations revealed that overexpression of mafr-1 can influence reproductive output (Khanna et al, 2014).…”

“…Characterization of a mafr-1 null mutant Previous studies of mafr-1 in C. elegans have utilized RNAi-based approaches (Khanna et al, 2014) and a gain-of-function allele of mafr-1 (Pradhan et al, 2017) leaving the true loss-of-function phenotype unknown. To better examine the biological functions of MAFR-1, we assessed the impact of a true molecular null allele of mafr-1, hereafter referred to as mafr-1 (KO) (Fig.…”

“…In light of the conflicting phenotypes associated with the loss of Maf1 by RNA interference (RNAi), genetic mutations in metazoans (Bonhoure et al, 2015;Khanna et al, 2014;Khanna et al, 2015;Pradhan et al, 2017;Rideout et al, 2012), and in cultured cell models (Palian et al, 2014), we characterized a loss-of-function allele in a second metazoan model. While mafr-1 (KO) C. elegans are generally healthy ( Fig.…”

Maf1 phenotypes and cell physiology

“…TOR inhibition and calorie restriction) lead to Maf1-dependent repression [11,14,43] while deletion of Maf1 in yeast reduces chronological lifespan [42,44]. The tm6082 allele removes the phylogenetically conserved box C region, including three of the four β-sheets that make up the central core of Maf1 along with additional sequences (a total of 79 amino acids) and introduces 37 different amino acids in their place [42,45,46]. Interestingly, rather than shortening lifespan, the tm6082 mutant extended lifespan under both normal and calorie-restricted conditions.…”

“…Lifespan extension in the tm6082 mutant was also suppressed by Maf1 overexpression demonstrating that the phenotype is due to a loss of Maf1 function. Curiously, other phenotypes identified using the tm6082 allele in a different study were interpreted as resulting from a gain of function [45]. It is not clear how to reconcile these observations as neither study examined the levels of Maf1 mRNA or protein in the tm6082 mutant.…”