Metastasis suppressor 1 interacts with protein tyrosine phosphatase receptor-δ to regulate adipogenesis

MTSS1: beyond the integration of actin and membrane dynamics

MTSS1 is a ubiquitously expressed intracellular protein known mainly for its involvement in basic cellular processes, such as the regulation of actin organization and membrane architecture. MTSS1 has attracted much attention for its role as a tumor suppressor, being absent or expressed at reduced levels in advanced and metastasizing cancers. Occasionally, MTSS1 is, instead, upregulated in metastasis and, in some cases, even in primary tumors. In addition to these well-established functions of MTSS1 linked to its I-BAR- and WH2-domains, the protein is involved in modulating cell-cell contacts, cell differentiation, lipid metabolism, and vesicle formation and acts as a scaffolding protein for several E3 ubiquitin ligases. MTSS1 is classified as a housekeeping protein and is never mutated despite the several pathologic phenotypes linked to its dysregulation. Despite MTSS1's involvement in fundamental signaling pathways, MTSS1 gene ablation is not ubiquitously lethal, although it affects embryonic development. Due to MTSS1´s involvement in many seemingly disparate processes, with many cases lacking mechanistic explanations, we found it timely to review the recent data on MTSS1's role at the cellular level, as well as in health and disease, to direct further studies on this interesting multifunctional protein.

Cortactin controls bone homeostasis through regulating the differentiation of osteoblasts and osteoclasts

Cortactin (CTTN), a cytoskeletal protein and substrate of Src kinase, is implicated in tumor aggressiveness. However, its role in bone cell differentiation remains unknown. The current study revealed that CTTN was upregulated during osteoblast and adipocyte differentiation. Functional experiments demonstrated that CTTN promoted the in vitro differentiation of mesenchymal stem/progenitor cells into osteogenic and adipogenic lineages. Mechanistically, CTTN was able to stabilize the protein level of mechanistic target of rapamycin kinase (mTOR), leading to the activation of mTOR signaling. In-depth investigation revealed that CTTN could bind with casitas B lineage lymphoma-c (c-CBL) and counteract the function of c-CBL, a known E3 ubiquitin ligase responsible for the proteasomal degradation of mTOR. Silencing c-Cbl alleviated the impaired differentiation of osteoblasts and adipocytes caused by CTTN siRNA, while silencing mTOR mitigated the stimulation of osteoblast and adipocyte differentiation induced by CTTN overexpression. Notably, transplantation of CTTN-silenced bone marrow stromal cells (BMSCs) into the marrow of mice led to a reduction in trabecular bone mass, accompanied by a decrease in osteoblasts and an increase in osteoclasts. Furthermore, CTTN-silenced BMSCs expressed higher levels of receptor activator of nuclear factor κB ligand (RANKL) than control BMSCs did and promoted osteoclast differentiation when cocultured with bone marrow-derived osteoclast precursor cells. This study provides evidence that CTTN favors osteoblast differentiation by counteracting the c-CBL-induced degradation of mTOR and inhibits osteoclast differentiation by downregulating the expression of RANKL. It also suggests that maintaining an appropriate level of CTTN expression may be advantageous for maintaining bone homeostasis.

Genome-wide association study implicates lipid pathway dysfunction in antipsychotic-induced weight gain: multi-ancestry validation

Antipsychotic-induced weight gain (AIWG) is a common side effect of antipsychotic medication and may contribute to diabetes and coronary heart disease. To expand the unclear genetic mechanism underlying AIWG, we conducted a two-stage genome-wide association study in Han Chinese patients with schizophrenia. The study included a discovery cohort of 1936 patients and a validation cohort of 534 patients, with an additional 630 multi-ancestry patients from the CATIE study for external validation. We applied Mendelian randomization (MR) analysis to investigate the relationship between AIWG and antipsychotic-induced lipid changes. Our results identified two novel genome-wide significant loci associated with AIWG: rs10422861 in PEPD (P = 1.373 × 10-9) and rs3824417 in PTPRD (P = 3.348 × 10-9) in Chinese Han samples. The association of rs10422861 was validated in the European samples. Fine-mapping and functional annotation revealed that PEPD and PTPRD are potentially causal genes for AIWG, with their proteins being prospective therapeutic targets. Colocalization analysis suggested that AIWG and type 2 diabetes (T2D) shared a causal variant in PEPD. Polygenic risk scores (PRSs) for AIWG and T2D significantly predicted AIWG in multi-ancestry samples. Furthermore, MR revealed a risky causal effect of genetically predicted changes in low-density lipoprotein cholesterol (P = 7.58 × 10-4) and triglycerides (P = 2.06 × 10-3) caused by acute-phase of antipsychotic treatment on AIWG, which had not been previously reported. Our model, incorporating antipsychotic-induced lipid changes, PRSs, and clinical predictors, significantly predicted BMI percentage change after 6-month antipsychotic treatment (AUC = 0.79, R2 = 0.332). Our results highlight that the mechanism of AIWG involves lipid pathway dysfunction and may share a genetic basis with T2D through PEPD. Overall, this study provides new insights into the pathogenesis of AIWG and contributes to personalized treatment of schizophrenia.