OS is the most common bone malignancy in children and adolescents, and is also the leading cause of disability and death in this age-group [31]. Although adjuvant chemotherapy can improve patient prognosis, the long-term survival rate of patients after relapse remains less than 20% [32]. Many studies have shown that autophagy-related proteins are closely related to the prognosis of patients with OS. Low expression of AGT5 may be related to the poor prognosis of OS patients [33]. Silencing the autophagy-promoting gene BECN1 will increase cancer cell metastasis [13]. Currently, hundreds of proteins are thought to be involved in the autophagy process. In view of the importance of autophagy in OS, it can be reasonably speculated that autophagy-related genes have broad prospects in predicting prognosis, and multi-gene signatures generated by reliable algorithms will be superior to single molecules in predicting the prognosis of OS patients. In this study, for the first time, we integrated the genetic chip sequencing data of OS samples from the TARGET and GTEx databases with normal muscle tissue samples through bioinformatics methods to construct a prognostic autophagy-related gene signature for identifying prognostic OS biomarkers.
A total of 120 DEARGs were screened in this study. GO results showed that the BP of DEARGs mainly involved autophagy, macroautophagy, autophagosome assembly, autophagosome organization, and autophagy of mitochondrion; the CC were mainly enriched in autophagosome, phagophore assembly site, autophagosome membrane, vacuolar membrane, and late endosome; and the MF mainly involves ubiquitin protein ligase binding, chaperone binding, protein serine/ threonine kinase activity, and heat shock protein binding. Previous studies have shown that autophagy [33], macroautophagy [10], autophagosome [34], chaperone binding [35], threonine kinase activity [36], and heat shock protein binding [37] are closely related to the occurrence, invasion, and transfer of OS. KEGG pathway enrichment analysis showed that the enriched pathway mainly involved autophagy, mitophagy, and apoptosis. Studies have shown that autophagy plays an important role in the proliferation, invasion, metastasis, apoptosis, and drug resistance of OS [38, 39]. The role of mitophagy has been widely studied and is considered to be an early manifestation of cellular autophagy; mitochondrial function is impaired after mitochondrial damage and induces mitophagy [40]. Mei et al. [41] showed that mitophagy is involved in the proliferation and apoptosis of OS cell lines. Parunya et al. [42] showed that endoplasmic reticulum protein 29 (ERp29) expression was significantly higher in OS cells and was negatively correlated to patient survival time. All these findings are consistent with the data mining results of the present study.
BECN1, ATG7, ATG12, PIK3C3, GABARAP, GABARAPL1, GABARAPL2, MAP1LC3A, MAP1LC3B, and SQSTM1 are the hub autophagy-related genes identified in this study. BECN1 affects the drug sensitivity of OS cells by mediating the autophagy process [43]. ATG12 is involved in osteosarcoma cell metastasis [44], and ATG7 is associated with the invasiveness of bladder cancer cells [45]. The expression level of PIK3C3 in breast cancer gradually increases with disease progression [46], and low expression of GABARAPL1 is associated with poor prognosis in patients with breast cancer and hepatocellular carcinoma [47, 48]. The accumulation of MAP1LC3A in the nucleus of cancer cells is closely related to the poor prognosis of non-small cell lung cancer [49], and the low expression of MAP1LC3B is related to the poor prognosis of breast cancer [50]. High SQSTM1 expression is associated with poor prognosis in human acute lymphoblastic leukemia [51]. Taken together, the above studies support our analysis, but the role of these genes in OS is unclear. Considering the similarity of hub autophagy-related genes in CC and MF, we sorted by semantic similarity and found that MAP1LC3B, GABARAPL2, GABARAPL1, and GABARAP are the genes with the closest interaction. As members of the GABARAP family, GABARAP, GABARAPL1, and GABARAPL2 are widely involved in intracellular transport and autophagy pathways [48]. This further illustrates the reliability of the analysis results of this study.
Univariate Cox regression and Lasso Cox regression analysis showed that a gene signature composed of 9 autophagy-related genes (BNIP3, MYC, BAG1, CALCOCO2, ATF4, AMBRA1, EGFR, MAPK1, and PEX3) was closely related to the prognosis of OS. Studies have shown that the abnormal expression of MYC [52], ATF4 [53], and MAPK1 [54] is related to the proliferation, migration, and invasion of OS cells. As a transcription target of MYC, BAG1 cooperates with HSP70 molecular chaperone to selectively mediate MYC overexpression and affect the survival of OS cells [55]. The abnormal expression of BNIP3 is associated with the prognosis of renal cancer [56], breast cancer [57], and salivary adenoid cystic carcinoma [16]. Abnormal expression of AMBRA1 is associated with prognosis of bile duct cancer and cutaneous melanoma [58, 59]. Xiang et al. [60] showed that abnormal expression of EGFR is related to drug resistance in tumor patients. Chu et al. [61] showed that PEX3 is related to the invasion and metastasis of ovarian cancer cells. Importantly, our results show that the prognostic autophagy-related gene signature is significantly associated with OS metastasis, but not with age and gender. The autophagy-related gene signature revealed in this study are closely related to the clinical prognosis of OS patients, which may have important significance for the prognostic management and monitoring of these patients.
Current research on the prognosis of OS is mainly based on the prognosis of single genes, and the signature of multiple genes could well avoid the differences caused by individual heterogeneity. We used univariate Cox analysis, Lasso Cox, and survival analysis to predict the prognosis of OS patients by including multiple genes as a whole, and further verified by clinical correlation analysis. Therefore, this prognostic model has high prognostic value. However, our research has certain limitations. We used the recently opened TARGET database. Although it contains relatively complete clinical information of OS patients, this database lacks control group sample data. Therefore, the number of control group samples used in this study was derived from the GTEx database, which may lead to the data having a certain heterogeneity. In addition, there is currently an insufficient dataset to further verify the accuracy of our analysis results. Therefore, large-scale analysis of clinical tissue specimens is required in the future.