ER/Golgi trafficking is facilitated by unbranched actin filaments containing Tpm4.2

Kee, Anthony J.; Bryce, Nicole S.; Yang, Lingyan; Polishchuk, Elena; Schevzov, Galina; Weigert, Roberto; Polishchuk, Roman; Gunning, Peter W.; Hardeman, Edna C.

doi:10.1002/cm.21405

Cited by 11 publications

(7 citation statements)

References 56 publications

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“…The fact that basal proANP secretion by atrial myocytes lacking PAM resembled proANP secretion by Golgicide A-treated control myocytes suggested that inhibition of GBF1 prevented PAM from carrying out its normal role in the secretion of proANP by atrial myocytes, and that PAM affected proANP handling early in the secretory pathway. Blebbistatin, a myosin II-specific inhibitor (54), blocks tropomyosin 4.2-dependent ER to Golgi trafficking in mouse embryonic fibroblasts (55) and BFA-induced retrograde cis-Golgi to ER trafficking in pheochromocytoma cells (56). Blebbistatin had no effect on the rate at which proANP was secreted by either control or Pam Myh6-cKO/cKO myocytes (Fig.…”

Section: Resultsmentioning

confidence: 90%

Peptidylglycine α-amidating monooxygenase is required for atrial secretory granule formation

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et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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The discovery of atrial secretory granules and the natriuretic peptides stored in them identified the atrium as an endocrine organ. Although neither atrial nor brain natriuretic peptide (ANP, BNP) is amidated, the major membrane protein in atrial granules is peptidylglycine α-amidating monooxygenase (PAM), an enzyme essential for amidated peptide biosynthesis. Mice lacking cardiomyocyte PAM (PamMyh6-cKO/cKO) are viable, but a gene dosage-dependent drop in atrial ANP and BNP content occurred. Ultrastructural analysis of adult PamMyh6-cKO/cKO atria revealed a 13-fold drop in the number of secretory granules. When primary cultures of Pam0-Cre-cKO/cKO atrial myocytes (no Cre recombinase, PAM floxed) were transduced with Cre-GFP lentivirus, PAM protein levels dropped, followed by a decline in ANP precursor (proANP) levels. Expression of exogenous PAM in PamMyh6-cKO/cKO atrial myocytes produced a dose-dependent rescue of proANP content; strikingly, this response did not require the monooxygenase activity of PAM. Unlike many prohormones, atrial proANP is stored intact. A threefold increase in the basal rate of proANP secretion by PamMyh6-cKO/cKO myocytes was a major contributor to its reduced levels. While proANP secretion was increased following treatment of control cultures with drugs that block the activation of Golgi-localized Arf proteins and COPI vesicle formation, proANP secretion by PamMyh6-cKO/cKO myocytes was unaffected. In cells lacking secretory granules, expression of exogenous PAM led to the accumulation of fluorescently tagged proANP in the cis-Golgi region. Our data indicate that COPI vesicle-mediated recycling of PAM from the cis-Golgi to the endoplasmic reticulum plays an essential role in the biogenesis of proANP containing atrial granules.

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Section: Resultsmentioning

confidence: 90%

Peptidylglycine α-amidating monooxygenase is required for atrial secretory granule formation

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Luxmi

Powers

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…Tropomyosin Co-localizes with Most Actin Structures Tropomyosins have been implicated in a variety of different actin structures, including stress fibers [6], lamellipodia [7], granules [11], endosomes [12], cortical actin [13], the epithelial zonula adherens [14], podosomes [15], the cleavage furrow of dividing cells [16,17], mitotic spindles [16], actin ruffles [18], short microfilaments associated with the Golgi [16,19], filopodia [8], and the endoplasmic reticulum [20]. Mammalian cells can produce over 40 different splice variants using four different tropomyosin genes, TPM1-4, and the resulting gene products can be divided into low-molecular-weight (LMW) isoforms that span six actin monomers and high-molecular-weight (HMW) isoforms that span seven actin monomers.…”

Section: Resultsmentioning

confidence: 99%

Co-polymers of Actin and Tropomyosin Account for a Major Fraction of the Human Actin Cytoskeleton

et al. 2018

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Tropomyosin proteins form stable coiled-coil dimers that polymerize along the α-helical groove of actin filaments [1]. The actin cytoskeleton consists of both co-polymers of actin and tropomyosin and polymers of tropomyosin-free actin [2]. The fundamental distinction between these two types of filaments is that tropomyosin determines the functional capability of actin filaments in an isoform-dependent manner [3-9]. However, it is unknown what portion of actin filaments are associated with tropomyosin. To address this deficit, we have measured the relative distribution between these two filament populations by quantifying tropomyosin and actin levels in a variety of human cell types, including bone (U2OS); breast epithelial (MCF-10A); transformed breast epithelial (MCF-7); and primary (BJpar), immortalized (BJeH), and Ras-transformed (BJeLR) BJ fibroblasts [10]. Our measurements of tropomyosin and actin predict the saturation of the actin cytoskeleton, implying that tropomyosin binding must be inhibited in order to generate tropomyosin-free actin filaments. We find the majority of actin filaments to be associated with tropomyosin in four of the six cell lines tested and the portion of actin filaments associated with tropomyosin to decrease with transformation. We also discover that high-molecular-weight (HMW), unlike low-molecular-weight (LMW), tropomyosin isoforms are primarily co-polymerized with actin in untransformed cells. This differential partitioning of tropomyosins is not due to a lack of N-terminal acetylation of LMW tropomyosins, but it is, in part, explained by the susceptibility of soluble HMW tropomyosins to proteasomal degradation. We conclude that actin-tropomyosin co-polymers make up a major fraction of the human actin cytoskeleton.

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“…The Arp2/ 3 complex NPF WHAMM can bind microtubules and membranes and is enriched at the ERGIC and cis-Golgi 140 , but recent studies have linked WHAMM more with autophagy 141,142 . Other recent findings have implicated a specific population of tropomyosin 4.2-coated actin filaments as being important for ER-to-Golgi trafficking in a manner independent of Arp2/3 complex, but dependent on myosin II 143 . More work is needed to define actin polymerization factors and their roles in ER-to-Golgi transport.…”

Section: Actin and Er Structure/functionmentioning

confidence: 95%

Multiple roles for actin in secretory and endocytic pathways

2021

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ER/Golgi trafficking is facilitated by unbranched actin filaments containing Tpm4.2

Cited by 11 publications

References 56 publications

Peptidylglycine α-amidating monooxygenase is required for atrial secretory granule formation

Peptidylglycine α-amidating monooxygenase is required for atrial secretory granule formation

Co-polymers of Actin and Tropomyosin Account for a Major Fraction of the Human Actin Cytoskeleton

Multiple roles for actin in secretory and endocytic pathways

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