Renal cell carcinoma (RCC) is the one of the most common malignant tumor, and KIRC is the most common pathological subtype which account for about 75% of RCC. There are abundant blood vessels around KIRC, which enables KIRC to grow rapidly and transfer through blood vessels. Previous reports have demonstrated that more than 15% of patients with RCC have distant metastasis at the time of diagnosis . The effect of surgical treatment of localized KIRC is good, but the prognosis of patients with metastasis or recurrence is serious. Therefore, we can learn from it that one of the ways to improve the treatment and diagnosis of advanced metastatic KIRC is to screen biomarkers of KIRC progress, such as OSBPL. Previous studies have indicated that KIRC is connected with a variety of genes, such as SAA1, TBC1D3 and TICRR etc –.
The present study is the first to research the connection between OSBPL gene family and KIRC, including their expression, methylation and prognostic values. Our study found that in addition to OSBPL8, the high expression of most OSBPL family members represents the poor prognosis of KIRC patients, and the expression of individual OSBPL family members (such as osbpl5 and osbpl7) in KIRC patients is higher than that in normal people. Through the use of HPA, we found that their increased expression level will make patients more prone to tumors with higher malignancy, stage and status. Although gene mutations have very close relation with tumor occurrence and usually represent poor prognosis, we can see that the mutation of most OSBPL family members does not account for a high proportion in KIRC through the analysis of the family, and there is no data to show that their changes will lead to poor prognosis. So, in order to deeply understand the reasons for these phenomena, we made further research on the methylation, immune and function of OSBPL family members. The research showed that hypermethylation of OSBPL family members at some sites suggested high expression, which indicated the high expression of PD-L1 gene. The result was the decrease of CD8 + T cells and CD4 + T cells and the increase of Treg cells, resulting in immunosuppression. In addition, the study also shows that the high expression of some OSBPL family members often causes tumor angiogenesis through a variety of pathways, suggesting the deterioration of patients' condition.
In our study, we found an interesting phenomenon: the UaLcan database indicated that the expression of OSBPL3 and OSBPL6 genes in KIRC patients was lower than the expression in normal controls, but the OncoLnc database suggested that the high expression of OSBPL3 and OSBPL6 had connection with the poor prognosis of KIRC patients. By consulting the literature related to OSBPL3 and OSBPL6 gene, we did not find the exact explanation, but through the in-depth study of OSBPL3, we found many phenomena related to OSBPL3, which may explain the phenomenon of high expression but poor prognosis. In the literature on the relationship between these two genes and other cancers, we can see the role of OSBPL3 and OSBPL6: The top three tumors which have the strongest association between immune cell infiltration and OSBPL3 expression were BRCA, COAD and KIRC, respectively . In gastric cancer, OSBPL3 may regulate cell cycle progression in gastric cancer cells through R-Ras / Akt signaling pathway. Knockout of OSBPL3 in GC cells can reduce the level of R-Ras in GC cells, indicating that its R-Ras / Akt signaling pathway is down regulated . The OSBPL6 gene shows a binding site with miR-33a/b, a microRNA that shows a role in the regulation of FA β-oxidized genes have a targeted effect, which lead to a significantly lower level of β-hydroxybutyrate . In addition, the structural analysis results of OSBPL3 and OSBPL6, especially OSBPL3 gene, may also explain this interesting phenomenon to some extent: In Sumana's study, we learned that all OSBPL gene family members contain a core OSBPL-related domain (ORD), and many family members also contain pleckstrin homology (PH) domain, endoplasmic reticulum (ER) - targeted FFAT motifs, transmembrane ankyrin repeat sequence and / or GOLD domain . Furthermore, other studies have also shown that OSBPL family uses at least four non-mutually exclusive mechanisms for lipid metabolism, vesicular transport, cell signal transduction in cells and no vesicular lipid transport. ERK also plays an important role in the process of cell signal transduction. The regulation ERK by OSBPL helps to regulate the changes of gene expression due to the change of cell cholesterol level . In the research related to OSBPL3, we found that OSBPL3 has made a variety of changes to its own domain. For example, the S251, S273 and S426 sites in the pleckstrin homologous domain of OSBPL3 show a high phosphorylation level in multiple tumors. In addition, the frequent mutations of OSBPL3 and the changes of x676_splicing / v676g in its domain are also related to the survival of tumor cells . This characteristic of OSBPL3 may explain why there is a low expression in KIRC but high expression of OSBPL3 represents poor prognosis.
Furthermore, by using OncoLnc and HPA analysis, we gradually learned the association between the expression of OSBPL5 and OSBPL7 and the poor prognosis and immunohistochemistry of KIRC. In our study, we found that OSBPL5 and OSBPL7 are closely related to KIRC, which may indicate that OSBPL5 and OSBPL7 can be used as potential biomarkers of KIRC. However, the exact regulatory mechanisms of OSBPL5 and OSBPL7 in KIRC remain unclear. Therefore, we studied the mechanism of OSBPL5 and OSBPL7 in other cancers, and hope to find the possible mechanism of KIRC. We found that OSBPL5 is the downstream target of miR-526b-3p in non-small cell lung cancer, which can be absorbed by LMCD1-AS1, and LMCD1-AS1 can accelerate the invasion, migration and proliferation of NSCLC cells by regulating OSBPL5 . In addition, some studies have found that compounds which target OSBPL7 can increase ABCA1 dependent cholesterol outflow and protect renal function in two kidney disease models (chronic kidney disease and diabetic kidney disease) . Moreover, we also studied and analyzed the structure of OSBPL5, and found that OSBPL5 is a tail anchored endoplasmic reticulum membrane protein, which plays a role as a lipid transporter in the inner membrane. Due to its ORD domain, ER-anchored OSBPL5 can be used as a phosphatidylserine transporter. Some mutated residues in the ORD domain of OEBPL5 can bind to PS and PIP, transfer PIP to the endoplasmic reticulum and PS from the endoplasmic reticulum to the plasma membrane . This may explain why OSBPL5 is highly expressed in KIRC or even more tumors and represents a signal of poor prognosis.
In addition, the regulation of tumor immune microenvironment is a significant and attractive therapeutic target in the study of tumor progression. Previous immunotherapy studies have indicated that the tumor microenvironment of cancer can be widely divided into tumor infiltrating lymphocytes (TILs) (hot) or non-TILs (cold). It is fortunate for us that KIRC is a hot tumor . In KIRC TME, immune infiltrating cells include B cells, mast cells, matrix cells and neutrophils. These cells can affect the balance of KIRC-related immune escape and antitumor immunity . In our study, by using the TIMER 2.0 platform, it is not difficult to find that most OSBPL families have no significant difference or negative correlation with B cells, but have positive correlation with most other immune cells. CD4 + T cells can inhibit the growth of tumor cells by targeting the surface antigen of tumor cells, while the activated number of CD8 + T cells is often positively correlated with the good prognosis of various cancers. However, in the process of tumor progression, it will lose its immunogenicity, and the T cell response will also be inhibited by the tumor microenvironment. This inhibition involves regulatory T cells, which secrete immunosuppressive cytokines and myeloid and stromal cells. They regulate immune checkpoints by activating co-inhibitory receptors on T cells (such as PD-1, Tim-3 and CTLA-4), resulting in depletion of T cell phenotype and loss of function . In addition, some members of OSBPL family can also control the phagocytosis of macrophages, and its overexpression in macrophages often indicates a poor prognosis ,. These results suggest that the high expression of some OSBPL gene family members may cause the infiltration of more immunocompetent cells in the tumor microenvironment, which seems to indicate that hot tumors have more immune checkpoints. They may play a potential role in the immune microenvironment and may benefit from the interference of immunotherapy.