Differential Ser phosphorylation of vasodilator-stimulated phosphoprotein regulates colon tumor formation and growth

The Role of Vasodilator-stimulated Phosphoproteins in the Development of Malignant Tumors

Vasodilator-stimulated phosphoprotein (VASP) is an actin-binding protein that includes three structural domains: Enabled/VASP homolog1 (EVH1), EVH2, and proline-rich (PRR). VASP plays an important role in various cellular behaviors related to cytoskeletal regulation. More importantly, VASP plays a key role in the progression of several malignant tumors and is associated with malignant cell proliferation, invasion, and metastasis. Here, we have summarized current studies on the impact of VASP on the development of several malignant tumors and their mechanisms. This study provides a new theoretical basis for clinical molecular diagnosis and molecular targeted therapy.

Oncogenic BRAF noncanonically promotes tumor metastasis by mediating VASP phosphorylation and filopodia formation

BRAF is frequently mutated in various cancer types and contributes to tumorigenesis and metastasis. As an important switch in RAS signaling pathway, BRAF typically enables the activation of MEK and ERK, and its mutation significantly promotes metastasis. However, whether BRAF could stimulate metastasis via a distinct manner is still unknown. Herein, we found that a portion of the BRAF protein localized at the plasma membrane and that the BRAFV600E mutation led to abundant formation of filopodia, which is a hallmark of invasive cancer cells. Mechanistically, BRAF physically interacts with the pseudopod formation-related protein Vasodilator-stimulated phosphoprotein (VASP), and BRAF specifically catalyzes VASP phosphorylation at Ser157. VASP depletion or disruption of Ser157 phosphorylation preferentially reduced the motility, invasion and metastasis of tumor cells harboring oncogenic BRAF or KRAS. Moreover, in clinical cancer tissues, BRAFV600E was positively correlated with the extent of invasion, and tissues with BRAFV600E expression exhibited elevated levels of VASP Ser157 phosphorylation. Our study therefor reveals a noncanonical mechanism by which oncogenic BRAF or KRAS promotes metastasis, suggests that VASP Ser157 phosphorylation might serve as a valuable therapeutic target in BRAF or KRAS mutant cancers.

Protein kinase A Mediated Effects of Protein kinase C Partial Agonist HMI-1a3 in Colorectal Cancer Cells

Colorectal cancer is the third most commonly occurring cancer in men and the second in women. The global burden of colorectal cancer is projected to increase to over 2 million new cases with over 1 million deaths within the next 10 years and there is a great need for new compounds with novel mechanisms of action. Our group has developed PKC modulating isophthalic acid derivatives that induce cytotoxicity towards human cervical and prostate cancer cell lines. In this study, we investigated the effects of 5-(hydroxymethyl)isophthalate 1a3 (HMI-1a3) on colorectal cancer cell lines (Caco2, Colo205 and HT29). HMI-1a3 inhibited cell proliferation, decreased cell viability and induced an apoptotic response in all studied cell lines. These effects, however, were independent of PKC. Using serine/threonine kinome profiling and pharmacological kinase inhibitors we identified activation of the cAMP/PKA pathway as a new mechanism-of-action for HMI-1a3-induced anti-cancer activity in colorectal cancer cell lines. Our current results strengthen the hypothesis for HMI-1a3 as a potential anti-cancer agent against various malignancies. Significance Statement Colorectal cancer (CRC) is a common solid organ malignancy. Here, we demonstrate that the protein kinase C (PKC) C1 domain-targeted isophthalatic acid derivative HMI-1a3 has anti-cancer activity on CRC cell lines independently of PKC. We identified protein kinase A (PKA) activation as a mechanism of HMI-1a3 induced anti-cancer effects. Our results reveal a new anti-cancer mechanism of action for the partial PKC agonist HMI-1a3 and thus provide new insights for the development of PKC and PKA modulators for cancer therapy.