The 260-kDa transforming growth factor (TGF)-beta binding protein in rat glomeruli is a complex comprised of 170- and 85-kDa TGF-beta binding proteins

Advances and Challenges in Targeting TGF-β Isoforms for Therapeutic Intervention of Cancer: A Mechanism-Based Perspective

The TGF-β family is a group of 25 kDa secretory cytokines, in mammals consisting of three dimeric isoforms (TGF-βs 1, 2, and 3), each encoded on a separate gene with unique regulatory elements. Each isoform plays unique, diverse, and pivotal roles in cell growth, survival, immune response, and differentiation. However, many researchers in the TGF-β field often mistakenly assume a uniform functionality among all three isoforms. Although TGF-βs are essential for normal development and many cellular and physiological processes, their dysregulated expression contributes significantly to various diseases. Notably, they drive conditions like fibrosis and tumor metastasis/progression. To counter these pathologies, extensive efforts have been directed towards targeting TGF-βs, resulting in the development of a range of TGF-β inhibitors. Despite some clinical success, these agents have yet to reach their full potential in the treatment of cancers. A significant challenge rests in effectively targeting TGF-βs' pathological functions while preserving their physiological roles. Many existing approaches collectively target all three isoforms, failing to target just the specific deregulated ones. Additionally, most strategies tackle the entire TGF-β signaling pathway instead of focusing on disease-specific components or preferentially targeting tumors. This review gives a unique historical overview of the TGF-β field often missed in other reviews and provides a current landscape of TGF-β research, emphasizing isoform-specific functions and disease implications. The review then delves into ongoing therapeutic strategies in cancer, stressing the need for more tools that target specific isoforms and disease-related pathway components, advocating mechanism-based and refined approaches to enhance the effectiveness of TGF-β-targeted cancer therapies.

Protein kinase C and the development of diabetic vascular complications

Hyperglycemic control in diabetes is key to preventing the development and progression of vascular complications such as retinopathy, nephropathy and neuropathy. Increased activation of the diacylglycerol (DAG)-protein kinase C (PKC) signal transduction pathway has been identified in vascular tissues from diabetic animals, and in vascular cells exposed to elevated glucose. Vascular abnormalities associated with glucose-induced PKC activation leading to increased synthesis of DAG include altered vascular blood flow, extracellular matrix deposition, basement membrane thickening, increased permeability and neovascularization. Preferential activation of the PKCbeta isoform by elevated glucose is reported to occur in a variety of vascular tissues. This has lead to the development of LY333531, a PKCbeta isoform specific inhibitor, which has shown potential in animal models to be an orally effective and nontoxic therapy able to produce significant improvements in diabetic retinopathy, nephropathy, neuropathy and cardiac dysfunction. Additionally, the antioxidant vitamin E has been identified as an inhibitor of the DAG-PKC pathway, and shows promise in reducing vascular complications in animal models of diabetes. Given the overwhelming evidence indicating a role for PKC activation in contributing to the development of diabetic vascular complications, pharmacological therapies that can modulate this pathway, particularly with PKC isoform selectivity, show great promise for treatment of vascular complications, even in the presence of hyperglycemia.

Homodimers of the 60 kDa phosphatidylinositol-anchored transforming growth factor-beta 2 binding proteins in FBHEC and MG-63 cells

Phophatidylinositol (PI) anchored TGF-beta 2 binding proteins of approximately 60 and 140 kDa were recently identified in MG-63 human osteogenic sarcoma and fetal bovine heart endothelial cells (FBHEC) (Cheifetz, S., Massagué, J. (1991) J. Biol. Chem. 266, 20767-20772). The relationship between these two PI-anchored TGF-beta 2 binding proteins was investigated. Specifically labeled bands of approximately 60 and 110 kDa were observed when 125I-TGF-beta 2 labeled FBHEC and MG-63 cells were separated by SDS-PAGE under non-reducing conditions. Partial proteolysis of the affinity labeled 60 and 110 kDa species yielded similar peptides. The integrity of the 110 kDa species under denaturing conditions is dependent on both disulfide bonds and chemical cross-linking: reduction of the 110 kDa species yielded an affinity labeled species co-electrophoresing with the 60 kDa band; cleavage of chemical cross-links in the 110 kDa complex yielded a labeled 60 kDa component. These results indicate that the 110 kDa affinity labeled species in FBHEC and MG-63 cells is a homodimer. Within this complex the binding protein monomers can be chemically cross-linked to opposite arms of the disulfide-linked TGF-beta 2 homodimer.