Iroquois homeobox transcription factor (Irx5) promotes G₁/S-phase transition in vascular smooth muscle cells by CDK2-dependent activation

Abstract

The Iroquois homeobox (Irx5) gene is essential in embryonic development and cardiac electrophysiology. Although recent studies have reported that IRX5 protein is involved in regulation of the cell cycle and apoptosis in prostate cancer cells, little is known about the role of IRX5 in the adult vasculature. Here we report novel observations on the role of IRX5 in adult vascular smooth muscle cells (VSMCs) during proliferation in vitro and in vivo. Comparative studies using primary human endothelial cells, VSMCs, and intact carotid arteries to determine relative expression of Irx5 in the peripheral vasculature demonstrate significantly higher expression in VSMCs. Sprague-Dawley rat carotid arteries were subjected to balloon catherization, and the presence of IRX5 was examined by immunohistochemistry after 2 wk. Results indicate markedly elevated IRX5 signal at 14 days compared with uninjured controls. Total RNA was isolated from injured and uninjured arteries, and Irx5 expression was measured by RT-PCR. Results demonstrate a significant increase in Irx5 expression at 3–14 days postinjury compared with controls. Irx5 genetic gain- and loss-of-function studies using thymidine and 5-bromo-2′-deoxyuridine incorporation assays resulted in modulation of DNA synthesis in primary rat aortic VSMCs. Quantitative RT-PCR results revealed modulation of cyclin-dependent kinase inhibitor 1B (p27kip1), E2F transcription factor 1 (E2f1), and proliferating cell nuclear antigen (Pcna) expression in Irx5-transduced VSMCs compared with controls. Subsequently, apoptosis was observed and confirmed by morphological observation, caspase-3 cleavage, and enzymatic activation compared with control conditions. Taken together, these results indicate that Irx5 plays an important role in VSMC G1/S-phase cell cycle checkpoint control and apoptosis.

Discovery of a Robust Gene Regulatory Network with a Complex Transcription Factor Network on Organ Cancer Cell-line RNA Sequence Data

“…As for a FOSB down-regulation effect, further investigation will be needed to understand how the down regulation of FOSB plays a role in cancer cell development. This hypothesis is further supported by the results of others showing that TEAD4 [27][28][29][30], HMGA1 [31][32][33][34], and IRX5 [35][36][37] are related to cell proliferation, cell cycle mechanisms, and cancer development. Other than these genes, some genes in our intersection sub-network are also involved in cell proliferation mechanisms, such as FOXM1 [38], MYBL2 [39], and the SOX transcription family [40,41].…”

IRX5 promotes colorectal cancer metastasis by negatively regulating the core components of the RHOA pathway

“…Given the relationship between IRX5 and overall survival in patients with CRC, we believe that IRX5 plays an important role in the later stages of the disease. Taking into consideration the previous studies have shown that IRX5 participates in cell cycle and tumorigenesis . It appears that IRX5 is involved in the entire process of CRC.…”

“…Taking into consideration the previous studies have shown that IRX5 participates in cell cycle and tumorigenesis. 23,24 It appears that IRX5 is involved in the entire process of CRC.…”

“…A previous study showed that IRX5 promoted G1/S‐phase transition in vascular smooth muscle cells via CDK2‐dependent activation, and IRX5 negatively regulated the transforming growth factor β (TGF‐β) pathway, thus promoting the transformation of adenoma to cancer . These findings suggest that IRX5 may play an important role in the early stages of CRC.…”

IRX5 prompts genomic instability in colorectal cancer cells

“…DNA-binding motif with a length of 60 amino acids called the homeodomain. 3 In mammals, we divided six genes of the Iroquois into two homologous clusters, IRXA (IRX1, IRX4, and IRX5) and IRXB (IRX2, IRX3, and IRX6) which had the position on chromosome 8 and chromosome 16, respectively. 4 In previous research, Iroquois proteins have a vital function in early embryonic patterning, cell-type specification as well as tumorigenesis, either as activators or repressors.…”