The early diagnosis of CRC and timely surgery support a good prognosis, but approximately 25% of CRC cases are already advanced at the time of diagnosis [19]. Some still have surgical opportunities after neoadjuvant radiotherapy to reduce the clinical stage, and supplementation with targeted therapy or immunotherapy significantly prolongs survival [20]. Therefore, CRC survival can be improved by means of precision therapy regardless of disease stage, and CRC is curable if early diagnosis can be achieved. Thus, early diagnostic molecular marker screening is particularly important, and molecular target selection provides a reliable basis for targeted therapy. Thus, CRC molecular markers have become a research hotspot in recent years.
The results of this study showed that OSBPL3 expression was significantly higher in CRC tissues than in paraneoplastic tissues and correlated with the degree of CRC differentiation; the lower the CRC differentiation, the higher the OSBPL3 mRNA and protein expression, which is consistent with the results of existing studies and biochemical predictions [14]. It has also been shown that the degree of differentiation does not directly correlate with OSBPL3 expression, but rather the prognosis differs between groups with high and low expression in tumors with different degrees of differentiation [16]. In the weighted gene correlation network analysis (WGCNA) study, OSBPL3 was identified as a pivotal gene in CRC, with upregulated expression in cancer tissues, and its high expression correlated with a poor prognosis in CRC [21]. The results of the present study support the association of OSBPL3 with CRC development and progression. OSBP and OSBP-associated proteins (ORPs) constitute a large family of genes with sterol/lipid transport and regulatory activities involved in the control of lipid metabolism, regulation of vesicular transport and cell signaling events [22, 23]. ORP4, ORP5 and many other members of the ORP family have also been associated with tumors. ORP4 promotes the survival of rapidly proliferating cells [24] and is considered a potential marker of solid tumor dissemination and a poor prognosis [25]. Highly spliced variants leading to small changes in mRNA structure have been identified in several ORPs, including ORP1, ORP3 and ORP6 [26]. Differential mRNA splicing may result in functionally different forms of ORP3 genes [11]. Jiao et al. confirmed that OSBPL3 promotes the proliferation, migration, and motility of CRC cells by ex vivo experiments [14].
In the present study, we found that those who overexpressed OSBPL3 in CRC had correspondingly high expression of Ki-67, and there was a positive correlation between them. Ki-67 is a nuclear DNA-binding protein expressed in all vertebrates and is a proliferation marker widely used for tumor grading [27]. Ki-67 is present in the G1, S, and G2 phases of the cell cycle and is commonly used as a marker of cell proliferation [28]. Immunohistochemical detection of the Ki-67 index in tumors can objectively reflect the proliferation of tumors and is well established for clinical application. A high Ki-67 index usually indicates active proliferation and poor prognosis [29]. One study confirmed that the positive expression of Ki-67 in colorectal cancer increased with a decrease in differentiation [30]. High Ki-67 expression indicates a lower survival rate and is a predictor of CRC progression [31]. In this study, we concluded that OSBPL3 and Ki-67 expression were correlated and that OSBPL3 also had a similar pro-proliferative effect on CRC, which was positively correlated with the degree of differentiation. Therefore, it was further hypothesized that OSBPL3 and Ki-67 have the same pro-proliferative function and that high OSBPL3 expression is associated with a poor prognosis and could be used as a marker of CRC cell proliferation.
This study also found that KRAS mutations were more common in cases with high OSBPL3 expression, and the two were closely related. However, there was no clear relationship between OSBPL3 expression levels and KRAS mutation subtypes. Considering the effect of the small sample size, the variation in mutant subtypes needs further validation. RAS is an oncogene that plays a crucial role in cell proliferation, differentiation, growth and development [8]. Cyclin D1, the downstream target gene of its downstream signaling pathway Ras/Raf pathway, is a key factor in controlling cell proliferation from G1 to S phase and ultimately promoting cell proliferation [32]. It has been suggested that OSBPL3 is an R-Ras interacting oxysterol-binding protein homolog that regulates cell adhesion and plays a role in promoting tumor cell proliferation, migration and invasion, and evidence was obtained that the OSBPL3-VAPA complex stimulates R-Ras signaling [17]. It can regulate cytoskeleton reconstruction, alter the shape of CRC cells and the number of laminar pseudopods, and promote the motility and migration of CRC cells [14]. KRAS mutations are common driver mutations in CRC and are found at different frequencies in all consensus molecular subtypes (CMSs) [33]. KRAS mutation status has been used as a "molecular" predictor of efficacy for targeted therapy with epidermal growth factor receptor monoclonal antibody and has become class I evidence for clinical treatment. Patients with wild-type and G13D-mutant phenotypes can benefit from this type of drug therapy [9]. A new generation of KRAS mutation inhibitors has been used in the clinic; the first KRAS inhibitor sotorasib (AMG510) [34] became available in 2019, and the FDA approved adagrasib (MRTX849) for patients with the KRAS G12C mutation in 2021 [35]. Recent studies have defined the gene expression changes triggered by RAS [36]. However, mutated KRAS interacts with OSBPL3, and although it has been shown to affect the RAS pathway, some complementary signaling pathways can also play an important role in tumorigenesis progression [37], but this remains to be elucidated in future studies. The high level of OSBPL3 expression indicates that it may be a primary screening indicator for KRAS-mutated patients receiving KRAS inhibitors, and if the sample size is large enough, the clinicopathological characteristics of patients with KRAS mutations and high OSBPL3 expression can be analyzed to better characterize them. Mutations in the NRAS gene were not detected in this study. This may be because the proportion of NRAS mutations in CRC is approximately 2% -6% [38], which is much lower than that of KRAS. Additionally, there are limitations in the detection methods, as next-generation sequencing (NGS) methods detected RAS mutations in approximately 13% more patients [39]. The RAS pathway signature is superior to KRAS mutation status in predicting the dependence on RAS signaling [40]. Therefore, mutations in other members of the RAS pathway, not just the RAS gene, may play the same role in signaling. OSBPL3 may also be regulated by non-RAS pathways; for example, lncRNA MIR4435-2HG may regulate OSBPL3 expression via pathways such as the P38/MAPK pathway and the VEGF pathway [41]. Therefore, it is speculated that OSBPL3 does not facilitate colorectal carcinogenesis exclusively through the RAS pathway. Furthermore, although there is a correlation between KRAS mutations and OSBPL3, it is unclear whether OSBPL3 affects tumor biology regardless of KRAS status. This also deserves further study.