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Updated: Feb 13, 2026
Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
Published on: May 3, 2018
The non-neuronal cyclin-dependent kinase 5 is a fibrotic mediator potentially implicated in systemic sclerosis and a
Jun Wei1, Roberta G Marangoni1, Feng Fang1
1Northwestern Scleroderma Program, Department of Medicine, Feinberg School of Medicine, Chicago, IL, USA.
Abstract:
The mechanisms underlying persistent fibroblast activation and myofibroblast phenoconversion in underlying multi-organ fibrosis in systemic sclerosis (SSc) remain incompletely understood, hindering effective therapies to slow or reverse the process. Cyclin-dependent kinase 5 (CDK5) is a pleiotropic member of the CDK family originally identified in neuronal cells. In contrast to other CDKs, CDK5 activity depends on its CDK5R1 subunit p35. Here we demonstrate that expression of p35 and CDK5 activity are induced by TGF-ß in fibroblasts and adipocytic cell types. Levels of p35 are markedly elevated in both SSc skin biopsies and explanted SSc fibroblasts, as well as in fibrotic skin in mice. Ectopic p35 and CDK5 suppressed adipogenic markers while stimulating collagen production and myofibroblast markers, whereas RNAi-mediated CDK5 knockdown abrogated TGF-β fibrotic responses in a Smad-independent manner. Pharmacological inhibitors of CDK5 likewise prevented and reversed TGF-β responses in fibroblast monolayers and in ex vivo human skin organ cultures, ameliorated collagen overproduction in SSc fibroblasts, and prevented and reversed skin fibrosis in two distinct mouse models of SSc. Together, these results reveal a previously unrecognized key function for p35/CDK5 as a mediator of mesenchymal cell fibrotic responses. The results suggest a potential pathogenic role for elevated p35 expression and CDK5 activity in SSc, and raise the possibility that their selective pharmacological targeting might represent a novel treatment approach in fibrosis.
Insights
Elevated p35 and Cyclin-dependent kinase 5 (CDK5) drive fibrosis in systemic sclerosis (SSc). Targeting CDK5 may offer a novel therapeutic strategy for SSc and other fibrotic diseases.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Fibrosis in systemic sclerosis (SSc) involves persistent fibroblast activation, but underlying mechanisms are unclear.
- Therapies to slow or reverse SSc-related fibrosis are limited.
- Cyclin-dependent kinase 5 (CDK5), dependent on its p35 subunit, is implicated.
Purpose of the Study:
- To investigate the role of p35 and CDK5 in fibroblast activation and myofibroblast differentiation in SSc.
- To explore the potential of targeting p35/CDK5 as a therapeutic strategy for SSc fibrosis.
Main Methods:
- Assessed p35 and CDK5 expression and activity in SSc patient samples and mouse models.
- Utilized RNA interference (RNAi) to knockdown CDK5.
- Employed pharmacological CDK5 inhibitors in cell cultures and ex vivo human skin organ cultures.
- Evaluated effects on adipogenic and myofibroblast markers, and collagen production.
- Tested inhibitors in mouse models of SSc skin fibrosis.
Main Results:
- p35 and CDK5 expression/activity were induced by TGF-ß in fibroblasts and adipocytes.
- Elevated p35 levels were found in SSc skin biopsies and fibroblasts, and in mouse fibrotic skin.
- Ectopic p35/CDK5 suppressed adipogenesis while promoting collagen production and myofibroblast markers.
- CDK5 knockdown abrogated TGF-ß fibrotic responses independently of Smad signaling.
- CDK5 inhibitors prevented and reversed TGF-ß responses, reduced collagen in SSc fibroblasts, and ameliorated skin fibrosis in mouse models.
Conclusions:
- p35/CDK5 acts as a key mediator of fibrotic responses in mesenchymal cells.
- Elevated p35 and CDK5 activity likely play a pathogenic role in SSc.
- Selective pharmacological targeting of p35/CDK5 presents a potential novel therapeutic approach for fibrosis.
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