ccRCC is a common subtype of RCC, with high incidence, poor prognosis, strong invasiveness and frequent metastasis rate (Xie Y et al. 2017), most patients do not achieve a good prognosis (Xia Y et al.2017). Therefore, it is very important to study the molecular mechanisms of the development of ccRCC and find effective biomarkers to assist diagnosis, as well as provide corresponding molecular therapeutic targets. TAGLN2 is involved in actin cytoskeleton remodeling (Liu J et al. 2020). Numerous cancer-related mechanisms of migration, proliferation, differentiation, and apoptosis involve this protein either directly or indirectly. The carcinogenic effect of TAGLN2 has been widely reported in recent years (Zhang Y et al. 2010; Haijian et al. 2018; Jin H et al. 2021).
In this work, we discovered that TAGLN2 was highly overexpressed in ccRCC and other Pan-Cancer analyses based on TCGA database analysis. TAGLN2 can lead to worse clinical stage, pathological grade and survival prognosis of ccRCC patients. The prognostic analysis model constructed with TAGLN2 as the analysis variable has good accuracy for the long-term survival rate of ccRCC patients. Therefore, we believe that TAGLN2 has a significant value in assessing the prognosis of ccRCC patients. Subsequently, the effect of TAGLN2 on tumor immune infiltration deserves further study, Treg cells and Th2 cells were significantly positively correlated with TAGLN2 expression. In the tumor microenvironment, Treg cells are considered to be the main factor that helps tumor cells evade immune surveillance (Watson M et al. 2021), Th2 immune skewing can promote distant metastasis of tumors (Jma B et al. 2022). Therefore, TAGLN2 may be implicated in regulating the expression level of immune cells in the tumor microenvironment and inducing immune escape.
In vitro studies showed that TAGLN2 silencing decreased the proliferation, colony formation, migration, invasion, and EMT of ccRCC cell lines. A statistical difference was found in Bcl-2 and Bax but no significant change in Caspase-3 by examining the expression of apoptosis related proteins. Anti-apoptotic protein Bcl-2 and pro-apoptotic protein Bax are upstream signals of apoptosis, which could be blocked in the process of downward propagation. Therefore, the apoptotic executive protein caspase-3 does not change. So, TAGLN2 silencing may affect apoptosis, but does not trigger apoptosis, obviously. EMT is closely associated with loss of E-cadherin expression and upregulation of mesenchymal-related proteins like N-cadherin and Vimentin (Jolly M K et al. 2017). we found that, after TAGLN2 silencing, EMT was reversed. So, silencing TAGLN2 can inhibit the development of EMT and reduce the distant metastasis ability of tumor cells.
Studies on the role of the PI3K/AKT pathway in tumor development and spread are extensive (Li Y et al. 2016). It is indispensable in regulating cancer cells growth, migration, apoptosis and survival (J Chen et al. 2011; Brian M Slomovitz et al. 2012; Popolo A et al. 2017). In recent renal cancer studies, inhibition of PI3K/AKT signaling pathway was found to reduce cancer cell proliferation (Lin H et al. 2021), migration (Peng X S et al. 2020), invasion (Chen P et al. 2019), EMT (Chen H et al. 2019) and promote cell apoptosis (Zhang S et al. 2017). In this study, the PI3K/AKT signaling pathway was first identified by enrichment analysis of TAGLN2-related differential genes. Subsequent WB analysis conformed that the activity of this signaling pathway was significantly reduced after TAGLN2 silencing. The above experimental results may lead to the speculation that TAGLN2 may promote ccRCC cell proliferation, migration, invasion, and EMT by stimulating the PI3K/AKT signaling pathway, while inhibiting apoptosis. This study suggests that TAGLN2 is promising as a target for ccRCC treatment.
In this papre, there are still some deficiencies. Firstly, we only discussed the effects of TAGLN2 on ccRCC cells in vitro, but the effects of TAGLN2 on tumor size, weight, proliferation and apoptosis in the subcutaneous tumorigenesis model of nude mice need to be confirmed by further experiments. Secondly, whether there are direct acting protein between TAGLN2 and PI3K/AKT signaling pathways that affect the activity this pathway also deserves to be explored in subsequent experments. Finally, the overexpression of TAGLN2 was insufficient in this study to further verify its influence and mechanism on the malignant biological behavior of 786-O and CAKI-1 cell lines.