Differential regulation of cellular functions by the C-termini of transmembrane 4 L six family proteins in 2- or 3-dimensional environment

Abstract

The transmembrane 4 L six family proteins TM4SF1, TM4SF4, and TM4SF5 share 40-50% overall sequence identity, but their C-terminus identity is limited. It may be likely that the C-termini of the members are important and unique for own regulatory functions. We thus examined how the TM4SF5 C-terminus affected cellular functions differentially from other family members. Using colon cancer cells expressing wildtype (WT), C-terminus-deleted, or chimeric mutants, diverse cellular functions were explored in 2-dimensional (2D) and 3-dimensional (3D) condition. The C-termini of the proteins were relatively comparable with respect to 2D cell proliferation, although each C-terminal-deletion mutant exhibited increased proliferation relative to the WT. Using chimeric constructs, we found that the TM4SF5 C-terminus was critical for regulating the diverse metastatic functions of TM4SF5, and could positively replace the C-termini of other family members. Replacement of the TM4SF1 or TM4SF4 C-terminus with that of TM4SF5 increased spheroids growth, transwell migration, and invasive dissemination from spheroids in 3D collagen gels. TM4SF5-mediated effects required its extracellular loop 2 linked to the C-terminus via the transmembrane domain 4, with causing c-Src activation. Altogether, the C-terminus of TM4SF5 appears to mediate pro-migratory roles, depending on a structural relay from the second extracellular loop to the C-terminus.

Transmembrane 4 L Six Family Member 5 Senses Arginine for mTORC1 Signaling

“…Interestingly, TSAHC treatment blocked TM4SF5-L-arginine binding in the lysosomal lumen and abolished the TM4SF5-mTOR interaction that would occur in the cytosol. Therefore, the TM4SF5 LEL domain may have an allosteric relay from the LEL to the cytosolic C terminus during its influence in intracellular signaling, as previously suggested (Cheong et al, 2017). Furthermore, the effects of TSAHC emphasize the significance of arginine sensing by TM4SF5 during HCC growth, although SLC38A9 and Castor1 also have capacities to sense arginine following arginine sufficiency (Wang et al, 2015;Wyant et al, 2017).…”

Role of Transmembrane 4 L Six Family 1 in the Development and Progression of Cancer

“…This interaction might be critical for the biological function of TM4SF1 because syntenin-1 is involved in cancer cell proliferation and migration (Sarkar, 2004). TM4SF1, TM4SF4, and TM4SF5 share 40-50% overall sequence identity and their C-terminal sequences differ substantially (Cheong et al, 2017).…”

“…By using chimeric constructs, Jin-Gyu Cheong et al reported that the C-terminus of TM4SF5 played an important role to regulate the diverse metastatic functions, and could positively replace the C-termini of TM4SF1 or TM4SF4, which increased the ability of cancer cell proliferation migration, and invasion (Cheong et al, 2017). However, the cytoplasmic or extracellular regions of TM4SF1 substituted by corresponding sequences of TM4SF5 did not prevent localisation of the chimeric proteins to Lamp2-positive organelles (Lekishvili et al, 2008).…”

TM4SF5-Mediated Roles in the Development of Fibrotic Phenotypes

“…Furthermore, the structural aspect or relay from the N -glycosylated LEL to the cytosolic C-terminus through the 4th transmembrane domain appears to be critical for TM4SF5-mediated signaling activation of FAK and c-Src [17]. Cysteines proximal to transmembrane domains are involved in palmitoylation that is critical for the association of TM4SF5 with tetraspanins and other receptors [6].…”

“…Cysteines proximal to transmembrane domains are involved in palmitoylation that is critical for the association of TM4SF5 with tetraspanins and other receptors [6]. Meanwhile, TM4SF1 and TM4SF4, which are also transmembrane 4 L six family members, differ from TM4SF5 in the ability to activate FAK and/or c-Src to regulate migration [17]. Although TM4SF5 alone can modulate signaling pathways, it can also collaborate with other membrane proteins and receptors to control intracellular signaling pathways.…”