The interaction of protein-tyrosine phosphatase α (PTPα) and RACK1 protein enables insulin-like growth factor 1 (IGF-1)-stimulated Abl-dependent and -independent tyrosine phosphorylation of PTPα

The c-Abl-RACK1-FAK signaling axis promotes renal fibrosis in mice through regulating fibroblast-myofibroblast transition

BACKGROUND

Renal fibrosis is a prevalent manifestation of chronic kidney disease (CKD), and effective treatments for this disease are currently lacking. Myofibroblasts, which originate from interstitial fibroblasts, aggregate in the renal interstitium, leading to significant accumulation of extracellular matrix and impairment of renal function. The nonreceptor tyrosine kinase c-Abl (encoded by the Abl1 gene) has been implicated in the development of renal fibrosis. However, the precise role of c-Abl in this process and its involvement in fibroblast-myofibroblast transition (FMT) remain poorly understood.

METHODS

To investigate the effect of c-Abl in FMT during renal fibrosis, we investigated the expression of c-Abl in fibrotic renal tissues of patients with CKD and mouse models. We studied the phenotypic changes in fibroblast or myofibroblast-specific c-Abl conditional knockout mice. We explored the potential targets of c-Abl in NRK-49F fibroblasts.

RESULTS

In this study, fibrotic mouse and cell models demonstrated that c-Abl deficiency in fibroblasts mitigated fibrosis by suppressing fibroblast activation, fibroblast-myofibroblast transition, and extracellular matrix deposition. Mechanistically, c-Abl maintains the stability of the RACK1 protein, which serves as a scaffold for proteins such as c-Abl and focal adhesion kinase at focal adhesions, driving fibroblast activation and differentiation during renal fibrosis. Moreover, specifically targeting c-Abl deletion in renal myofibroblasts could prove beneficial in established kidney fibrosis by reducing RACK1 expression and diminishing the extent of fibrosis.

CONCLUSIONS

Our findings suggest that c-Abl plays a pathogenic role in interstitial fibrosis through the regulation of RACK1 protein stabilization and myofibroblast differentiation, suggesting a promising strategy for the treatment of CKD.

NB-3 expression in endothelial cells contributes to the maintenance of blood brain barrier integrity in a mouse high-altitude cerebral edema model

NB-3, a member of the contactin/F3 subgroup in the immunoglobulin superfamily, plays an important role in neural development and injury recovery. The blood brain barrier (BBB) is typically involved in the pathophysiology of neural disorders, such as hypoxic-ischemic brain injury. Our previous research found that NB-3 protects against brain damage in a mouse stroke model. However, its role in high-altitude disorders caused by hypobaric hypoxia exposure remains unknown. In the present study, we found that NB-3 was expressed in brain microvascular endothelial cells (BMECs) and responded to hypoxia stimulation. Conditional knockout of NB-3 in endothelial cells increased BBB leakage and downregulated tight junction proteins in vivo. NB-3 deficiency promoted the downregulation of tight junction proteins under Lipopolysaccharide (LPS)/hypoxia stimulation. Conversely, overexpression or supplementation with NB-3 alleviated endothelial barrier injuries. Transcriptome sequencing showed that NB-3 regulated various cell attachment genomic changes, including the Notch signaling pathway. Blocking the Notch signaling pathway increased VEGF/VEGFR2 pathway activation induced by LPS/hypoxia. Collectively, we present evidence that NB-3 plays key roles in maintaining BBB integrity under high-altitude cerebral edema conditions.

RACK1 promotes lung cancer cell growth via an MCM7/RACK1/ Akt signaling complex

MCM7, a member of the miniature chromosome maintenance (MCM) protein family, is crucial for the initiation of DNA replication and proliferation in eukaryotic cells. In this report, we demonstrate that RACK1 regulates cell growth and cell cycle progression in human non-small-cell lung cancer by mediating MCM7 phosphorylation through an MCM7/RACK1/Akt signaling complex. RACK1 functions as a central scaffold that brings Akt into physical proximity with MCM7. Overexpression of RACK1 increases interactions between Akt and MCM7 and promotes Akt-dependent MCM7 phosphorylation, which in turn increases MCM7 binding to chromatin and MCM complex formation. Together, these changes promote DNA replication and cell proliferation. Our findings reveal a novel signaling pathway that regulates growth in non-small cell lung cancer.

PTPα is required for laminin-2-induced Fyn-Akt signaling to drive oligodendrocyte differentiation

Extrinsic signals that regulate oligodendrocyte maturation and subsequent myelination are essential for central nervous system development and regeneration. Deficiency in the extracellular factor laminin-2 (Lm2), as occurs in congenital muscular dystrophy, can lead to impaired oligodendroglial development and aberrant myelination, but many aspects of Lm2-regulated oligodendroglial signaling and differentiation remain undefined. We show that receptor-like protein tyrosine phosphatase alpha (PTPα) is essential for myelin basic protein expression and cell spreading during Lm2-induced oligodendrocyte differentiation. PTPα complexes with the Lm2 receptors α6β1 integrin and dystroglycan to transduce Fyn activation upon Lm2 engagement. In this way, PTPα mediates a subset of Lm2-induced signals required for differentiation that includes mTOR-dependent Akt activation but not Erk activation. We identify N-myc downstream regulated gene-1 (NDRG1) as a PTPα-regulated molecule during oligodendrocyte differentiation and distinguish Lm2 receptor-specific modes of Fyn-Akt-dependent and -independent NDRG1 phosphorylation. Altogether, this reveals a Lm2-regulated PTPα-Fyn-Akt signaling axis that is critical for key aspects of the gene expression and morphological changes that mark oligodendrocyte maturation.

Recent Advances in ADAM17 Research: A Promising Target for Cancer and Inflammation

Since its discovery, ADAM17, also known as TNFα converting enzyme or TACE, is now known to process over 80 different substrates. Many of these substrates are mediators of cancer and inflammation. The field of ADAM metalloproteinases is at a crossroad with many of the new potential therapeutic agents for ADAM17 advancing into the clinic. Researchers have now developed potential drugs for ADAM17 that are selective and do not have the side effects which were seen in earlier chemical entities that targeted this enzyme. ADAM17 inhibitors have broad therapeutic potential, with properties ranging from tumor immunosurveillance and overcoming drug and radiation resistance in cancer, as treatments for cardiac hypertrophy and inflammatory conditions such as inflammatory bowel disease and rheumatoid arthritis. This review focuses on substrates and inhibitors identified more recently for ADAM17 and their role in cancer and inflammation.