PIP3 depletion rescues myoblast fusion defects in human rhabdomyosarcoma cells

Abstract

Myoblast fusion is required for myotube formation during myogenesis, and defects in myoblast differentiation and fusion have been implicated in a number of diseases, including human rhabdomyosarcoma. Although transcriptional regulation of the myogenic program has been studied extensively, the mechanisms controlling myoblast fusion remain largely unknown. This study identified and characterized the dynamics of a distinct class of blebs, termed bubbling blebs, which are smaller than those that participate in migration. The formation of these bubbling blebs occurred during differentiation and decreased alongside a decline in phosphatidylinositol-(3,4,5)-trisphosphate (PIP3) at the plasma membrane before myoblast fusion. In a human rhabdomyosarcoma-derived (RD) cell line that exhibits strong blebbing dynamics and myoblast fusion defects, PIP3 was constitutively abundant on the membrane during myogenesis. Targeting phosphatase and tensin homolog (PTEN) to the plasma membrane reduced PIP3 levels, inhibited bubbling blebs and rescued myoblast fusion defects in RD cells. These findings highlight the differential distribution and crucial role of PIP3 during myoblast fusion and reveal a novel mechanism underlying myogenesis defects in human rhabdomyosarcoma.

Caspase-mediated nuclear pore complex trimming in cell differentiation and endoplasmic reticulum stress

“…The cytoplasmic-to-nuclear ratio of NES Rev -GFP, a widely used export probe, was significantly lower in myoblasts undergoing cell-cell fusion than in myotubes ( Figure 1D and E , and Figure 1—figure supplement 3D ). Similarly, the cytoplasmic-to-nuclear ratio of NES PKI -GFP significantly decreased when myoblasts started to produce “bubbling” blebs and became fusion-competent ( Figure 1—figure supplement 3E–G ; Lian et al, 2020 ). We also asked if the localization of α-tubulin is affected.…”

Actin filaments form a size‐dependent diffusion barrier around centrosomes

“…The approaches developed here have powerful applications beyond probing diffusion mechanisms. Chemically inducible dimerization systems have been widely used to spatiotemporally manipulate cellular architecture and signaling by recruiting proteins of interest (Rs of ≤ 5.8 nm) onto target sites in cells (Lin et al , 2013a; Leyton‐Puig et al , 2016; Fan et al , 2017; Hong et al , 2018; Lian et al , 2020). The current study has established a new system that enables rapid recruitment of proteins of interest onto the centriolar lumen, pericentriolar matrix, or centriolar satellites within seconds.…”