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Critical functions of FAM134 family members in endoplasmic reticulum remodeling, ER-phagy and collagen quality control

ABSTRACT: Degradation of the endoplasmic reticulum (ER) by selective autophagy (ER-phagy) is vital for cellular homeostasis. Here, we introduce FAM134A/RETREG2 and FAM134C/RETREG3 as new ER-phagy receptors. FAM134A and FAM134C exist in a relatively inactive state under basal conditions and require an activation signal to induce significant ER fragmentation. Molecular modeling and simulations implicate a single compact fold of FAM134A’s reticulon homology domain (RHD). In contrast, the RHDs of FAM134B and FAM134C are able to adopt at least three discrete conformations. These differences result in slower vesicle formation for FAM134A compared to FAM134C and mostly FAM134B. Global proteomic analyses of knockout MEFs indicate both distinct and overlapping roles for the Fam134s, with Fam134a being most distant from Fam134b and Fam134c. Fam134c appears to enhance and facilitate Fam134b’s role in maintaining pro-collagen-I levels and is therefore insufficient to compensate for its loss. By contrast, Fam134a has a particular mode of action in maintaining pro-collagen-I levels and is able to fully compensate loss of Fam134b or Fam134c upon over-expression in its wild-type or LIR mutant form.

INSTRUMENT(S): Q Exactive HF

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: carmine cirillo

LAB HEAD: Paolo Grumati

PROVIDER: PXD025626 | Pride | 2021-06-23

REPOSITORIES: Pride

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			Action	DRS
	2021-01-04_MS_PG_AR_U2OS_TrexFAM134A_01.raw	Raw
	2021-01-04_MS_PG_AR_U2OS_TrexFAM134A_02.raw	Raw
	2021-01-04_MS_PG_AR_U2OS_TrexFAM134A_03.raw	Raw
	2021-01-04_MS_PG_AR_U2OS_TrexFAM134A_04.raw	Raw
	2021-01-04_MS_PG_AR_U2OS_TrexFAM134A_DOX_01.raw	Raw

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An mTORC1-CK2 axis controls starvation induced ER-phagy via FAM134C

Project description:The degradation of endoplasmic reticulum (ER) via selective autophagy is driven by the ER-phagy receptors that facilitate the incorporation of ER-fragments into nascent autophagosomes. How these receptors are regulated, in response to ER-phagy-inducing stimuluses, is largely unknown. Here we propose that starvation, as well as mTOR inhibition, triggers ER-phagy primarily through the activation of the ER-phagy receptor FAM134C. In physiological, nutrient reach, conditions FAM134C is phosphorylated by the Casein kinase 2 (CK2) protein at specific residues negatively affecting FAM134C interaction with the LC3 proteins, thereby preventing ER-phagy. Pharmacological or starvation-induced mTORC1 inhibition limits phosphorylation of FAM134C by CK2, hence promoting FAM134C activation and ER-phagy. Moreover, inhibition of CK2 or the expression of a phospho-mutant FAM134C protein is sufficient to stimulate ER-phagy. Conversely, starvation induced ER-phagy is inhibited in cells and mice that lack FAM134C or expressing a phospho-mimetic FAM134C protein. Overall, these data describe a new mechanism regulating ER-phagy and provides an example of cargo selectivity mechanism during starvation induced autophagy.

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Proteome of Fam134A/B/C knock-out MEFs

Project description:Selective degradation of endoplasmic reticulum (ER) via autophagy receptors is important to maintain cell homeostasis. In this study we identify FAM134A/RETREG2 and FAM134C/RETREG3 as bona fide ER-phagy receptors containing a classical and functional LIR motif. In contrast to the other family member FAM134B/RETREG1, over-expressed FAM134A and C are in a relatively inactive state, under basal conditions, and require an activation signal to fragment significant amounts of ER. Global proteomes analysis of knockout MEFs suggests distinct and overlapping functions of the three FAM134. Common functions are the maintenance of the ER shape and delivery of mis-folded pro-collagen I to lysosomes. Single knockout of Fam134a or Fam134c lead to swollen ER and massive intracellular accumulation of pro-collagen I. In this context, Fam134a but not Fam134c over-expression is able to recover collagen I levels, in Fam134b knockout MEFs, indicating distinct modes of action. Moreover, we provide evidence that Fam134a has a LIR-independent function in maintaining collagen I homeostasis in a co-receptor complex together with Fam134c. This pathway works in parallel to Fam134b, which in contrast is self-sufficient to drive ER-phagy.

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Transcriptional regulation of FAM134B by TFEB/TFE3 controls ER-phagy in response to starvation and chondrocyte differentiation

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