Members of the MS4A family have similar structures and roles. Previous reports indicate that the MS4A protein predominantly interacts with several immunological receptors and controls signaling pathways [5, 6]. The well-known members of the MS4A family, namely MS4A1 (CD20), MS4A2 (FcεRIβ), and MS4A3 (HTm4), all have a significant role in cancer initiation and development. However, it is unknown how most members of this family contribute to lung adenocarcinoma.
To determine this, we started with exploring how the MSA4 family was expressed in lung adenocarcinoma. Using the TCGA database, we discovered that 12/18 genes in the MS4A family had differential expression. Based on our research of the prevalence of copy number variation and somatic mutation in the MS4A family, we found that the majority of the MS4A family members had gene mutations in lung adenocarcinoma. Specifically, MS4A14, MS4A4A, MS4A1, and MS4A3 genes had the highest prevalence of mutations. Additionally, we performed a function enrichment analysis. The findings corroborated prior research by Mattiola and Eon Kuek and revealed that the MS4A family was primarily involved in the receptor signaling pathway on the surface of immune response-regulating cells and the immune response-regulating signaling pathway, which was associated with immunoglobulin binding [5, 6]. According to their research, the MS4A family is instrumental in humoral immunity, IgE signal transduction, T cell proliferation control [20–22]. According to prognostic analyses, patients with low expression levels of MS4A2, MS4A4A, MS4A7, MS4A14, and MS4A15 had a worse prognosis. The overall survival of patients with lung adenocarcinoma was positively correlated with the expression level of these genes. Then, to better predict the overall survival of lung cancer patients, we built a prognostic model incorporating the five prognostic genes. Using the LASSO Cox regression analysis and prediction nomogram, we found that the model could predict 3- and 5-year overall survival with reasonable accuracy. During immune infiltration analyses, we discovered that prognostic genes and immune-infiltrating cells had a statistically significant positive correlation. This suggests that immunological modulation by the MS4A family contributes to the onset and progression of lung adenocarcinoma.
Notably, MS4A2, an intensively examined MS4A family member, is a crucial part of high-affinity IgE. In agreement with the findings of Ly et al., MS4A2 has low expression in lung adenocarcinomas and is associated with a bad prognosis [17]. Their findings show that mast cells affect the development of lung cancer and that high MS4A2 expression on stromal mast cells is a positive prognostic sign for the survival of early lung cancer patients. We discovered that as per the prognostic model and nomogram analysis findings, MS4A2 is a protective gene in lung adenocarcinoma and an independent factor impacting prognosis; it is also considerably positively associated with immune-infiltrating cells. Then, using RT-qPCR, we further confirmed MS4A2 expression in lung adenocarcinoma. Notably, only three of the nine sample pairs gathered herein showed reduced expression of MS4A2. In agreement with other research, our bioinformatics study showed that the level of MS4A2 was low in lung adenocarcinoma. This could be attributed to the small sample size of this study. Another influencing factor could have been the primers we created because we only chose a small portion of the MS4A2 mRNA, and this may not accurately reflect all functions of MS4A2. As the MS4A family’s first identified ion channel, MS4A2 can function as a calcium channel [23, 24], which is associated with the development of numerous cancers [25]. Although this could be a processes through which MS4A2 contributes to lung adenocarcinoma, more research is required to precisely determine the underlying pathway and mechanism.
Much of the MS4A4A research has been focused on the hematopoietic system [5]. Numerous recent studies have revealed a connection between MS4A4A and the incidence of Alzheimer's disease [26, 27]. We discovered from the TCGA database that MS4A4A expression was downregulated in lung adenocarcinoma and that the overall survival rate of lung adenocarcinoma patients with regulated MS4A4A expression was poor. The expression level of MS4A4A in lung adenocarcinoma was confirmed using RT-qPCR. Eight out of nine sample pairs demonstrated downregulated MS4A4A expression, which was in line with our expectations. Previous research revealed that MS4A4A was upregulated in gastric and ovarian cancer [12, 28], which was associated with a poor prognosis. In addition, some investigations revealed that the expression of MS4A4A and MS4A7 was upregulated in gliomas and that overall patient survival was low [13]. Additionally, MS4A4A was identified to be a surface marker of M2 macrophages, indicating that inhibiting MS4A4A could prevent the growth and operation of M2 macrophages [29]. These findings in lung adenocarcinoma contradict our predictions. However, some studies have indicated that MS4A4A can boost dectin-1-dependent NK cell-mediated anti-tumor metastasis and stimulate mast cell activation, which may be connected to the function of MS4A4A in lung adenocarcinoma [30, 31].
During the study of the MS4A family, it was discovered using PCR amplification that MS4A7 is primarily expressed in B cells and monocytes in hematopoietic cell lines. In addition, MS4A7 is present in non-hematopoietic cell types, such as those found in the colon, thymus, lung, and other organs [4, 6]. Few reports on MS4A7 in tumors have been published so far, mainly in cases of esophageal and gastric cancer [32, 33]. In their research, it has been discovered that the poor prognosis of these two cancers is associated with high MS4A7 expression. Even in lung adenocarcinoma, MS4A7 has been reported to be a predictor of poor survival [14]. In our study, however, the low expression of MS4A7 in lung adenocarcinoma suggests a bad prognosis. Our findings were further supported by the outcomes of RT-qPCR tests performed on lung cancer tissues and healthy lung tissues. In addition, the immune infiltration analysis revealed a strong correlation between MS4A7 and immune cells, particularly macrophages and dendritic cells, in lung adenocarcinoma. In contrast to our prediction results, which may be attributable to the various databases and analysis techniques used by us, Yu Luo et al. [14] reported MS4A7 as a predictor of poor lung adenocarcinoma; however, they did not analyze the expression level of MS4A7 in lung adenocarcinoma. The bad prognosis associated with high MS4A7 expression in gastric and esophageal cancers may be associated with the ability of MS4A7 to control tumor growth in lung adenocarcinoma through various other mechanisms; however, the specific mechanism of MS4A7 in lung adenocarcinoma remains to be confirmed.
Recent investigations have demonstrated that MS4A14 is highly expressed in renal clear cell carcinoma and that individuals with high MS4A14 expression had lower overall survival rates [34]. Conversely, patients with low expression of MSA14 in lung adenocarcinoma reportedly have a bad prognosis. The prognosis model has enabled us to determine that MS4A14 is a lung adenocarcinoma protective factor that is favorably correlated with patient survival time. However, the biological functions of MS4A14 remain poorly understood, and more research is required to determine how MS4A14 affects lung adenocarcinoma.
The MS4A family is closely related to calcium channels [5, 6], and MS4A15, which controls the level of calcium ions to coordinate lipid remodeling and prevent iron death, has recently been shown to be present in the endoplasmic reticulum [35]. According to several studies, MS4A15 is upregulated in ovarian cancer and can encourage the proliferation of ovarian cancer cells both in vivo and in vitro [15]. In our experiment, we found the expression of MS4A15 in lung cancer to be downregulated relative to that in normal lung tissues, indicating a negative prognosis for patients. Since MS4A15 is found in the endoplasmic reticulum, it possibly controls iron death and the structure and function of the mitochondria to influence the onset and progression of malignancies.
This study has some limitations. In vivo and in vitro tests are primarily lacking, and the mechanism behind the involvement of the MS4A family in lung adenocarcinoma remains to be identified.
In summary, we thoroughly examined the expression and prognosis of the MS4A family in lung adenocarcinoma and identified five MS4A family genes with prognostic value. Additionally, we found a strong association between prognostic genes and immune infiltration, and prognostic genes may influence lung adenocarcinoma development via calcium channels.