“The ubiquitin ligase SIAH2 is a female-specific regulator of circadian rhythms and metabolism”

Abstract

Circadian clocks enable organisms to predict and align their behaviors and physiologies to constant daily day-night environmental cycle. Because the ubiquitin ligase Siah2 has been identified as a potential regulator of circadian clock function in cultured cells, we have used SIAH2-deficient mice to examine its function in vivo. Our experiments demonstrate a striking and unexpected sexually dimorphic effect of SIAH2-deficiency on the regulation of rhythmically expressed genes in the liver. The absence of SIAH2 in females, but not in males, altered the expression of core circadian clock genes and drastically remodeled the rhythmic transcriptome in the liver by increasing the number of day-time expressed genes, and flipping the rhythmic expression from nighttime expressed genes to the daytime. These effects are not readily explained by effects on known sexually dimorphic pathways in females. Moreover, loss of SIAH2 in females, not males, preferentially altered the expression of transcription factors and genes involved in regulating lipid and lipoprotein metabolism. Consequently, SIAH2-deficient females, but not males, displayed disrupted daily lipid and lipoprotein patterns, increased adiposity and impaired metabolic homeostasis. Overall, these data suggest that SIAH2 may be a key component of a female-specific circadian transcriptional output circuit that directs the circadian timing of gene expression to regulate physiological rhythms, at least in the liver. In turn, our findings imply that sex-specific transcriptional mechanisms may closely interact with the circadian clock to tailor overt rhythms for sex-specific needs.

Lysine-independent ubiquitination and degradation of REV-ERBα involves a bi-functional degradation control sequence at its N-terminus

“…We and others have investigated how various ubiquitin ligases contribute to the degradation of REV-ERB and their effects on the circadian clock (12)(13)(14)(15)(16). In this study, we focused on trying to understand the central events that need to happen to REV-ERB protein itself for degradation to take place.…”

“…Lanes "M" were lysates from cells treated with MG132 for 3 hours (lanes 6, 12, 18, and 24). C. WT and the rearranged mutant AA2-9insAA25 were co-transfected with Sport6 (lanes 1-12) or Sport6-SPSB4 (lanes [13][14][15][16][17][18][19][20][21][22][23][24], into HEK293 cells. 36-48 hours after transfection, cells were treated with cycloheximide for the indicated number of hours, and the Western blot was probed with anti-REV-ERB antibody Lanes "M" were lysates from cells treated with MG132 for 4 hours (lanes 6, 12, 18, and 24).…”

“…Deleting AA2-9, the binding site of SPSB4, did not have much effect on ubiquitination of REV-ERB WT or delAA2-9 were transfected into HEK293 cells with ("+" lanes) or without ("-" lanes) cotransfection of a plasmid that expresses a HA-tagged ubiquitin (HA-Ub). Lysates from transfected cells (lanes 1-6) were immunoprecipitated (IP) with an anti-REV-ERB antibody (lanes 7-18) Western blots were probed with an anti-REV-ERB (lanes 1-12) or anti-HA antibody (lanes [13][14][15][16][17][18]. Bands that form a ladder are marked with a bracket on the right, representing REV-ERB proteins that have increasing number of ubiquitin attached.…”

Sex Inclusion in Transcriptome Studies of Daily Rhythms

“…In mice, 23 of 44 unique tissues had samples only from males, whereas 16 tissues had samples in some way from females (as female only, male and female, or mixed; Supplemental Table S7 ). Within liver, by far the most common tissue, 46 of 60 studies were male only, whereas 5 were female only and 5 were male and female ( Vollmers et al, 2009 ; Yang et al, 2016 ; Sato et al, 2017 ; Weger et al, 2019 ; Mekbib et al, 2022 ) ( Supplemental Table S8 ). In humans, the most common tissue was blood, for which 6 of 9 studies included males and females.…”

“…Second, the underrepresentation of females in transcriptome experiments was concordant with that of other experiments. Third, of the 9 studies that included males and females for any experiment, 2 reported results by sex ( Jouffe et al, 2022 ; Mekbib et al, 2022 ).…”