Lamin is essential for nuclear localization of the GPI synthesis enzyme PIG-B and GPI-anchored protein production in Drosophila

Abstract

Membrane lipid biosynthesis is a complex process that occurs in various intracellular compartments. In Drosophila, phosphatidylinositol glycan-B (PIG-B), which catalyzes addition of the third mannose in glycosylphosphatidylinositol (GPI), localizes to the nuclear envelope (NE). Although this NE localization is essential for Drosophila development, the underlying molecular mechanism remains unknown. To elucidate this mechanism, we identified PIG-Binteracting proteins by performing immunoprecipitation followed by proteomic analysis. We then examined which of these proteins are required for the NE localization of PIG-B. Knockdown of Lamin Dm0, a B-type lamin, led to mislocalization of PIG-B from the NE to the endoplasmic reticulum. Lamin Dm0 associated with PIG-B at the inner nuclear membrane, a process that required the tail domain of Lamin Dm0. Furthermore, GPI moieties were distributed abnormally in the Lamin Dm0 mutant. These data indicate that Lamin Dm0 is involved in the NE localization of PIG-B and is required for proper GPI-anchor modification of proteins.

PIGB maintains nuclear lamina organization in skeletal muscle of Drosophila

“…It has recently been reported that oxidoreductases and lipid synthases, which play a role in regulating cell growth and survival, are also localized in the NL ( Cheng et al, 2023 ), and their localization and function may be abnormal in PIGB mutants. We previously reported that PIGB binds to Lamin Dm0 ( Yamamoto-Hino et al, 2020 ), and overexpression of PIGB in this study affected the localization of Lamin Dm0. These results suggest that disruption of the NL in PIGB 13 is due to the impaired distribution of Lamin Dm0.…”

“…Moreover, the C-terminal Ig-fold regions of lamins are observed at 20 nm intervals on both sides of filaments ( Turgay et al, 2017 ). We have reported that the Ig-fold domain of Lamin Dm0 mainly binds to PIGB, while the other domains may slightly contribute to the association with PIGB ( Yamamoto-Hino et al, 2020 ). It is possible that PIGB acts as a support for Lamin Dm0 to spread the network homogenously with proper spacing via its C-terminal Ig-fold region.…”

“…Specifically, it catalyzes the addition of the third mannose. GPI is synthesized in the endoplasmic reticulum (ER) in mammalian cells; however, we previously reported that Drosophila PIGB localizes to the INM via Lamin Dm0 ( Yamamoto-Hino et al, 2018 , 2020 ). Although the expression of wild-type (WT) PIGB completely rescues the lethality of the PIGB mutant, the expression of ER-localized PIGB does not ( Yamamoto-Hino et al, 2018 ).…”