The glucose-sensing transcription factor MLX balances metabolism and stress to suppress apoptosis and maintain spermatogenesis

Abstract

Male germ cell (GC) production is a metabolically driven and apoptosis-prone process. Here, we show that the glucose-sensing transcription factor (TF) MAX-Like protein X (MLX) and its binding partner MondoA are both required for male fertility in the mouse, as well as survival of human tumor cells derived from the male germ line. Loss of Mlx results in altered metabolism as well as activation of multiple stress pathways and GC apoptosis in the testes. This is concomitant with dysregulation of the expression of male-specific GC transcripts and proteins. Our genomic and functional analyses identify loci directly bound by MLX involved in these processes, including metabolic targets, obligate components of male-specific GC development, and apoptotic effectors. These in vivo and in vitro studies implicate MLX and other members of the proximal MYC network, such as MNT, in regulation of metabolism and differentiation, as well as in suppression of intrinsic and extrinsic death signaling pathways in both spermatogenesis and male germ cell tumors (MGCTs).

Coordinated Cross-Talk Between the Myc and Mlx Networks in Liver Regeneration and Neoplasia

“… 25 , 37 ( B ) Relevant regions of the Mlx locus before and after CreER-mediated recombination showing the location of LoxP sites flanking coding exons 3 and 6. 8 ( C ) Verification of MlxKO and DKO. ( A–C ) Four to 5 weeks after CreER activation, DNA from the indicated livers was assessed for the presence of intact or recombined Myc and Mlx alleles.…”

“…The generation of mice bearing a 1717-bp deletion spanning exons 3–6 of the Mlx locus ( Mlx KO mice) ( Figure 1 B ) also has been described recently. 8 Transgenic mice expressing a fusion protein comprising the hormone-binding domain of CreER and under the control of the albumin promoter that allows CreER to be activated in hepatocytes after tamoxifen exposure (B6.129S2- Alb tm1(cre/ERT2)Mtz , MGI: 3052812 ) were a kind gift from Dr Frank Gonzalez (Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute). The latter mice were bred to homozygosity with Mlx LoxP/LoxP mice or Myc LoxP/LoxP × Mlx LoxP/LoxP mice.…”

“…c-Myc (Myc) is a Basic helix-loop-helix leucine zipper (bHLH-Zip) transcription factor that regulates numerous target genes, which collectively support survival, proliferation, metabolism, ribosome biogenesis and translation. 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 Positive regulation involves Myc’s direct sequence-specific DNA binding in heterodimeric association with its obligate bHLH-Zip partner, Max. 6 , 7 This occurs at canonical E-box elements that typically reside in the vicinity of proximal promoters.…”

“…The Myc Network crosstalks and shares considerable regulatory overlap with a structurally related but distinct group of bHLH-Zip transcription factors that comprise the so-called Mlx Network. 1 , 2 , 3 , 8 , 20 , 24 , 25 Classically believed to control target gene sets smaller and more functionally restricted than those overseen by Myc, the Myc-like equivalents of the Mlx Network include the transcription factors Carbohydrate response element (ChRE)-binding protein (ChREBP) and MondoA. Upon binding glucose and other nutrients, these cytoplasmic proteins translocate to the nucleus, heterodimerize with the Max-like protein Mlx, and bind to their target genes at carbohydrate response elements (ChoREs) comprising tandem E-boxes separated by 5 nucleotides.…”

Disruption of Multiple Overlapping Functions Following Stepwise Inactivation of the Extended Myc Network

“…The c-Myc (Myc) oncoprotein is a critical bHLH-ZIP transcription factor that regulates hundreds–thousands of target genes in association with its bHLH-ZIP partner protein Max [ 1 , 2 ]. Positive control is achieved via the direct binding of Myc–Max heterodimers to consensus E-box elements (CACGTG) that are usually located in proximity to transcriptional start sites [ 2 , 3 ].…”