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Phosphoinositide regulation of integrin trafficking required for muscle attachment and maintenance.

Ribeiro I, Yuan L, Tanentzapf G, Dowling JJ, Kiger A - PLoS Genet. (2011)

Bottom Line: Depletion of mtm leads to increased integrin turnover at the sarcolemma and an accumulation of integrin with PI(3)P on endosomal-related membrane inclusions, indicating a role for Mtm phosphatase activity in endocytic trafficking.The depletion of Class II, but not Class III, PI3-kinase rescued mtm-dependent defects, identifying an important pathway that regulates integrin recycling.Importantly, similar integrin localization defects found in human XLMTM myofibers signify conserved MTM1 function in muscle membrane trafficking.

View Article: PubMed Central - PubMed

Affiliation: Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California, United States of America.

ABSTRACT
Muscles must maintain cell compartmentalization when remodeled during development and use. How spatially restricted adhesions are regulated with muscle remodeling is largely unexplored. We show that the myotubularin (mtm) phosphoinositide phosphatase is required for integrin-mediated myofiber attachments in Drosophila melanogaster, and that mtm-depleted myofibers exhibit hallmarks of human XLMTM myopathy. Depletion of mtm leads to increased integrin turnover at the sarcolemma and an accumulation of integrin with PI(3)P on endosomal-related membrane inclusions, indicating a role for Mtm phosphatase activity in endocytic trafficking. The depletion of Class II, but not Class III, PI3-kinase rescued mtm-dependent defects, identifying an important pathway that regulates integrin recycling. Importantly, similar integrin localization defects found in human XLMTM myofibers signify conserved MTM1 function in muscle membrane trafficking. Our results indicate that regulation of distinct phosphoinositide pools plays a central role in maintaining cell compartmentalization and attachments during muscle remodeling, and they suggest involvement of Class II PI3-kinase in MTM-related disease.

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Class II and Class III PI3-kinases affect mtm-dependent integrin adhesions differently.(A–A′) Pharate abdominal muscles, F-actin. (A) IR-Pi3K68D and (A′) IR-Vps34 single RNAi (top) and mtm co-RNAi (bottom). Arrowheads, detached IOMs. (B) Number of visibly detached IOMs. (C, C′, C″) Sarcolemmal βPS-integrin detected at costameres; (C) control, (C′) IR-Pi3K68D and (C″) IR-Vps34 in single RNAi (top) and mtm co-RNAi (bottom). Only Pi3K68D, mtm co-RNAi restored βPS-integrin at costameres. (D) Percentage IOMs that lack costameres ≥half of myofiber surface. (E, E′, E″) βPS-integrin central z-sections; (E) control, (E′) IR-Pi3K68D and (E″) IR-Vps34 single RNAi (top) and mtm co-RNAi (bottom). Only Pi3K68D, mtm co-RNAi reverted abnormal βPS-integrin-inclusions. (F) Percentage IOMs with βPS-integrin on inclusions. (B,D,F) IOMs in single RNAi (light bars) and mtm co-RNAi (dark bars) conditions. Scale bars 10 µm, except A–A′ 200 µm.
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pgen-1001295-g005: Class II and Class III PI3-kinases affect mtm-dependent integrin adhesions differently.(A–A′) Pharate abdominal muscles, F-actin. (A) IR-Pi3K68D and (A′) IR-Vps34 single RNAi (top) and mtm co-RNAi (bottom). Arrowheads, detached IOMs. (B) Number of visibly detached IOMs. (C, C′, C″) Sarcolemmal βPS-integrin detected at costameres; (C) control, (C′) IR-Pi3K68D and (C″) IR-Vps34 in single RNAi (top) and mtm co-RNAi (bottom). Only Pi3K68D, mtm co-RNAi restored βPS-integrin at costameres. (D) Percentage IOMs that lack costameres ≥half of myofiber surface. (E, E′, E″) βPS-integrin central z-sections; (E) control, (E′) IR-Pi3K68D and (E″) IR-Vps34 single RNAi (top) and mtm co-RNAi (bottom). Only Pi3K68D, mtm co-RNAi reverted abnormal βPS-integrin-inclusions. (F) Percentage IOMs with βPS-integrin on inclusions. (B,D,F) IOMs in single RNAi (light bars) and mtm co-RNAi (dark bars) conditions. Scale bars 10 µm, except A–A′ 200 µm.

Mentions: A similar functional relationship was seen between Pi3K68D and mtm for roles related to integrin adhesions, as with viability. Importantly, Pi3K68D, but not Vps34, depletion rescued muscle detachment (Figure 5A, 5B) and loss of βPS-integrin localization at costameres (Figure 5C, 5C′, 5D) that occurs with loss of mtm function. Consistent with rescue of the IACs, co-depletion of mtm and Pi3K68D, and not Vps34, also eliminated the βPS-integrin- and Dlg-containing membrane inclusions (Figure 5E, 5E′, 5F, Figure S6E), indicating a functional relationship between the abnormal central inclusions and IACs at the sarcolemma. The testis visceral muscle function was also restored to normal with Pi3K68D and mtm co-depletion, implicating turnover of integrin-mediated adhesions in the gonadal muscle. Altogether, these results signify that Pi3K68D function mediates mtm RNAi mutant defects in maintenance of IACs, and suggest that Pi3K68D may synthesize a PI(3)P subpool co-regulated by Mtm important for integrin trafficking and localization.


Phosphoinositide regulation of integrin trafficking required for muscle attachment and maintenance.

Ribeiro I, Yuan L, Tanentzapf G, Dowling JJ, Kiger A - PLoS Genet. (2011)

Class II and Class III PI3-kinases affect mtm-dependent integrin adhesions differently.(A–A′) Pharate abdominal muscles, F-actin. (A) IR-Pi3K68D and (A′) IR-Vps34 single RNAi (top) and mtm co-RNAi (bottom). Arrowheads, detached IOMs. (B) Number of visibly detached IOMs. (C, C′, C″) Sarcolemmal βPS-integrin detected at costameres; (C) control, (C′) IR-Pi3K68D and (C″) IR-Vps34 in single RNAi (top) and mtm co-RNAi (bottom). Only Pi3K68D, mtm co-RNAi restored βPS-integrin at costameres. (D) Percentage IOMs that lack costameres ≥half of myofiber surface. (E, E′, E″) βPS-integrin central z-sections; (E) control, (E′) IR-Pi3K68D and (E″) IR-Vps34 single RNAi (top) and mtm co-RNAi (bottom). Only Pi3K68D, mtm co-RNAi reverted abnormal βPS-integrin-inclusions. (F) Percentage IOMs with βPS-integrin on inclusions. (B,D,F) IOMs in single RNAi (light bars) and mtm co-RNAi (dark bars) conditions. Scale bars 10 µm, except A–A′ 200 µm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3037412&req=5

pgen-1001295-g005: Class II and Class III PI3-kinases affect mtm-dependent integrin adhesions differently.(A–A′) Pharate abdominal muscles, F-actin. (A) IR-Pi3K68D and (A′) IR-Vps34 single RNAi (top) and mtm co-RNAi (bottom). Arrowheads, detached IOMs. (B) Number of visibly detached IOMs. (C, C′, C″) Sarcolemmal βPS-integrin detected at costameres; (C) control, (C′) IR-Pi3K68D and (C″) IR-Vps34 in single RNAi (top) and mtm co-RNAi (bottom). Only Pi3K68D, mtm co-RNAi restored βPS-integrin at costameres. (D) Percentage IOMs that lack costameres ≥half of myofiber surface. (E, E′, E″) βPS-integrin central z-sections; (E) control, (E′) IR-Pi3K68D and (E″) IR-Vps34 single RNAi (top) and mtm co-RNAi (bottom). Only Pi3K68D, mtm co-RNAi reverted abnormal βPS-integrin-inclusions. (F) Percentage IOMs with βPS-integrin on inclusions. (B,D,F) IOMs in single RNAi (light bars) and mtm co-RNAi (dark bars) conditions. Scale bars 10 µm, except A–A′ 200 µm.
Mentions: A similar functional relationship was seen between Pi3K68D and mtm for roles related to integrin adhesions, as with viability. Importantly, Pi3K68D, but not Vps34, depletion rescued muscle detachment (Figure 5A, 5B) and loss of βPS-integrin localization at costameres (Figure 5C, 5C′, 5D) that occurs with loss of mtm function. Consistent with rescue of the IACs, co-depletion of mtm and Pi3K68D, and not Vps34, also eliminated the βPS-integrin- and Dlg-containing membrane inclusions (Figure 5E, 5E′, 5F, Figure S6E), indicating a functional relationship between the abnormal central inclusions and IACs at the sarcolemma. The testis visceral muscle function was also restored to normal with Pi3K68D and mtm co-depletion, implicating turnover of integrin-mediated adhesions in the gonadal muscle. Altogether, these results signify that Pi3K68D function mediates mtm RNAi mutant defects in maintenance of IACs, and suggest that Pi3K68D may synthesize a PI(3)P subpool co-regulated by Mtm important for integrin trafficking and localization.

Bottom Line: Depletion of mtm leads to increased integrin turnover at the sarcolemma and an accumulation of integrin with PI(3)P on endosomal-related membrane inclusions, indicating a role for Mtm phosphatase activity in endocytic trafficking.The depletion of Class II, but not Class III, PI3-kinase rescued mtm-dependent defects, identifying an important pathway that regulates integrin recycling.Importantly, similar integrin localization defects found in human XLMTM myofibers signify conserved MTM1 function in muscle membrane trafficking.

View Article: PubMed Central - PubMed

Affiliation: Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California, United States of America.

ABSTRACT
Muscles must maintain cell compartmentalization when remodeled during development and use. How spatially restricted adhesions are regulated with muscle remodeling is largely unexplored. We show that the myotubularin (mtm) phosphoinositide phosphatase is required for integrin-mediated myofiber attachments in Drosophila melanogaster, and that mtm-depleted myofibers exhibit hallmarks of human XLMTM myopathy. Depletion of mtm leads to increased integrin turnover at the sarcolemma and an accumulation of integrin with PI(3)P on endosomal-related membrane inclusions, indicating a role for Mtm phosphatase activity in endocytic trafficking. The depletion of Class II, but not Class III, PI3-kinase rescued mtm-dependent defects, identifying an important pathway that regulates integrin recycling. Importantly, similar integrin localization defects found in human XLMTM myofibers signify conserved MTM1 function in muscle membrane trafficking. Our results indicate that regulation of distinct phosphoinositide pools plays a central role in maintaining cell compartmentalization and attachments during muscle remodeling, and they suggest involvement of Class II PI3-kinase in MTM-related disease.

Show MeSH
Related in: MedlinePlus