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Fam134c and Fam134b shape axonal endoplasmic reticulum architecture in vivo.

ABSTRACT: Endoplasmic reticulum (ER) remodeling is vital for cellular organization. ER-phagy, a selective autophagy targeting ER, plays an important role in maintaining ER morphology and function. The FAM134 protein family, including FAM134A, FAM134B, and FAM134C, mediates ER-phagy. While FAM134B mutations are linked to hereditary sensory and autonomic neuropathy in humans, the physiological role of the other FAM134 proteins remains unknown. To address this, we investigated the roles of FAM134 proteins using single and combined knockouts (KOs) in mice. Single KO in young mice showed no major phenotypes, however, combined Fam134b and Fam134c deletion (Fam134b/cdKO), but not the combination including Fam134a deletion, led to rapid neuromuscular and somatosensory degeneration, resulting in premature death. Fam134b/cdKO mice show rapid loss of motor and sensory axons in the peripheral nervous system. Long axons from Fam134b/cdKO mice exhibited expanded tubular ER with a transverse ladder-like appearance, whereas no obvious abnormalities were observed in cortical ER. Our study unveils critical roles of FAM134C and FAM134B in the formation of tubular ER network in axons of both motor and sensory neurons.

INSTRUMENT(S): Q Exactive HF

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Nerve Cord

SUBMITTER: Francescopaolo Iavarone

LAB HEAD: Francescopaolo Iavarone

PROVIDER: PXD050983 | Pride | 2024-06-24

REPOSITORIES: Pride

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			Action	DRS
	2023-07-24_MS_FI_Fam134b_KO_1.raw	Raw
	2023-07-24_MS_FI_Fam134b_KO_2.raw	Raw
	2023-07-24_MS_FI_Fam134b_KO_3.raw	Raw
	2023-07-24_MS_FI_Fam134b_KO_4.raw	Raw
	2023-07-24_MS_FI_Fam134b_KO_5.raw	Raw

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The function of ER-phagy receptors is regulated through phosphorylation-dependent ubiquitination pathways.

Project description:Selective autophagy of the endoplasmic reticulum (ER), known as ER-phagy, is an important regulator of ER remodeling and is critical to maintaining cellular homeostasis during environmental changes. We recently showed that members of the FAM134 family play a role during stress-induced ER-phagy. However, the mechanisms on how they are activated remain largely unknown. In this study, we analyzed mTOR-mediated phosphorylation of FAM134 as a trigger of FAM134-driven ER-phagy. An unbiased screen of kinase inhibitors revealed that CK2 is essential for ER-phagy driven by FAM134B and FAM134C after inhibition of mTOR. Using superresolution microscopy, we showed that CK2 activity is essential for the formation of high-density groups of FAM134B and FAM134C. Continually, the FAM134B and FAM134C proteins that carry point mutations of selected serine residues within their reticulon homology domain are unable to form high-density clusters. Furthermore, we provide evidence that ubiquitination regulates ER-phagy receptors and that dense clustering of FAM134B and FAM134C requires events upstream of ubiquitination. Treatment with the CK2 inhibitor SGC-CK2-1 or mutation of phosphosites prevents Torin1-induced ER-phagy flux as well as ubiquitination of FAM134 proteins, and consistently treatment with E1 inhibitor suppresses Torin1-induced ER-phagy flux. Therefore, we propose that CK2 dependent phosphorylation of ER-phagy receptors precedes ubiquitin-dependent activation of ER-phagy flux.

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