4.3 Identified molecular pathways in bladder cancer
Modification of different molecular pathways and changes in living organisms such as mutations, alterations in gene control and epigenetic alterations are the driving forces for malignancy and its development.96 Alterations of signaling pathways, metabolic pathways, cytoskeleton and DNA repair pathways have been identified to be associated with tumorigenesis and progression of different types of cancers.97 Moreover, signaling pathways that control cell growth, proliferation, cell specialization and apoptosis, when damaged could lead to carcinogenesis and disease progression.97-99 Activation of focal adhesion and MAPK signaling pathways and subsequent dysregulating genetic processes are further uncovered in the development of bladder cancer.100
Data generated by RNA sequencing and bioinformatics analyses revealed that 17 differentially expressed genes were down-regulated in 5637 cell line whereas 44 were up-regulated in comparison to T24.46 Similarly, down-regulation of WNT9A and WNT10A was confirmed in both cell lines which have been found to be associated with alteration of Wnt signaling pathways that contribute to bladder cancer initiation and development1,9 Using RNA-Seq, the most significantly enriched pathway involved in the development of bladder cancer was found to be the cell adhesion molecules (CAMs) pathway (FDR= 2.67E-08).101 Further enrichment of bladder cancer pathway, focal adhesion, and extracellular matrix (ECM) receptor interaction pathways revealed that genes such as PTPRF ,VEGFA and CLDN7 participated in all the pathways including bladder cancer.101 The upregulation of genes such asITGA , F3 , ANXA1 have been reported in cancer-related pathways associated with cell growth, cellular cycle and apoptosis. However, downregulation of GRB7 , VEGP genes was also noted in the same pathways.102
Further, upregulation of Interferon-g, angiogenesis, and inflammatory pathways was observed in NEURAL, mesenchymal-like (MES), and squamous-cell carcinoma-like (SCC).103 Nevertheless, downregulation of several DEGs have been reported in immune activation pathways like NF-kappa B signaling pathway, MAPK signaling pathway and PI3K-Akt signaling pathway.104 Interleukin-10 production, lymphocyte chemotaxis and aberrant IFNγ, NF-κB and ERK signalling networks are the major pathways identified in the immune transcriptome related to programmed death-ligand 1 (PD- L1) inhibitors status and may participate in the evasion of immunity in high- grade muscle invasive urothelial carcinoma of the bladder (HGUC).105 Similarly, PIK3/AKT/MTOR pathway is activated by ERBB2 and FGFR3 (types of receptor tyrosine kinases) and is found to control essential carcinogenesis stages and progression of tumour.106 In a different study, key signaling pathways including vascular endothelial growth factor (VEGF/VEGFR) pathway and PI3K-Akt-mTOR pathway were identified and have been linked to promote muscle-invasive bladder carcinoma. Also, through activation of Janus kinase-signal transducer and activator of transcription (JAK/STAT) signaling pathway, carcinogenesis of urothelial carcinoma was improved by Insulin-like growth factor binding protein 4–1 (IGFBP4–1). Upregulation of IGFBP4–1 in bladder tissue might play a significant role in the initiation and progression of bladder cancer.71 Similarly, L-type amino acid transporter 1 (LAT1) which transport leucine (essential amino acid) control mammalian Target of Rapamycin (mTOR) signaling pathway and has been linked to the initiation and progression of urothelial carcinoma.107
Interestingly, RNA-sequencing has shown significant upregulation (fold change > 2.0) of 1793 genes, on the other hand, downregulation of 1759 genes was recorded after knockdown of Methyltransferase-like 3 (METTL3), suggesting that methylation of METTL3 may halt the process of N6 -methyladenosine (m6A) methylation which could lead to progression of urothelial carcinoma.108 The functional enrichment analysis revealed that strong (significant) negative correlation was observed in MYC oncogene and TNF-α/NF-κB target genes pathways while strong positive correlation was noticed in other signaling pathways in relation to METTL3 knockout.108
Moreover, activation of RAS pathway was observed more in all BC159-T samples than TCGA-urothelial bladder carcinoma (TCGA- BLCA) samples.79 The alterations of DNA in urothelial carcinoma are controlled by the activation of the Ras–MEK–ERK and PI3 kinase–AKT–mTOR pathways either by tumour suppressor genes or oncogenes and thus, RB1-dependent G1-S cell cycle restriction point, anabolic metabolism, and cell survival RB1-dependent G1/S checkpoint, cell continuity (survival) and building aspect of metabolism (anabolism) regulate carcinogenesis through these pathways.109 In about 20% of muscle-invasive bladder neoplasm, mutation in fibroblast growth factor (FGFR3) was activated, triggering activation of receptor that encourage profuse growth through downstream activation of ERKs.109,110 Genetically altered FGFR3 (mutant FGFR3) has been reported to activate RAS-MAPK pathway which led to abnormal proliferation of cancer cells.106
Several attempts have been put in place to avert proliferation of cancer cells by targeting the specific molecular pathways for the development of bladder cancer. For example, anticancer drugs like infigratinib and dasatinib were used to target Erk1/2 and Src signalling pathways and thus overcome most resistance observed in cancer cells.111 Similarly, three combination of anticancer drugs (romidepsin + gemcitabine + cisplatin) have been used to target the ERK pathway by increasing the level of reactive oxygen species (ROS) which trigger cysteine-aspertic proteases (caspases) that played a vital role in cell apoptosis.112 Therefore, understanding integrated metabolomic and transcriptomic pathways related to bladder cancer could offer alternative ways for the treatment of bladder cancer.113