The TRIpartite Motifs (TRIM) protein family is composed of more than 70 known TRIM proteins in humans and mice, which are encoded by approximately 71 genes in humans.
The TRIpatite Motif is composed by three zinc-binding domains, a RING domain (R), a B-box type 1 (B1) and a B-box type 2 (B2), followed by a coiled-coil (CC) region [1][2]. Functionally, the RING finger domain is involved in the ubiquitination system, mediating the transfer of ubiquitin from E2-Ub ligase enzyme to its substrates: this domain is therefore a characteristic signature of many E3 ubiquitin ligases [3]. Genes encoding for TRIM proteins are present in all metazoans [4] and mutations in these genes are implicated in a variety of human diseases including cancer.
This is not surprising if we consider that TRIM family proteins are involved in a plethora of cellular functions, such as regulation of gene expression, signal transduction pathways, autophagy, cell growth, migration, protein stability through the ubiquitination system, regulation of development and immune response, effects on cell survival and metabolism and direct antiviral action. Alterations of TRIM expression levels represent biomarker and prognostic factors of specific cancers including osteosarcoma, gastric, liver, breast, ovarian, prostate, lung, cervical and CRC [5][6][7].
Depending on tumor type and on their deregulation mechanisms, TRIMs proteins can exert their action both as onco-protein and tumor-suppressor proteins in cancers. To date, many TRIMs proteins have resulted to be overexpressed in one or more cancers. TRIMs 11, 14, 22, 24, 25, 27, 28, 32, 37, 44, 47, 49, 59, 65 are upregulated in some of the high incidence cancers (breast, gastric, liver, lung, osteosarcoma, prostate, kidney) [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49], while some others TRIM are upregulated in a cancer-specific way (e.g., TRIM22 in lung, TRIM31 and TRIM35 in liver, TRIM63 in breast, TRIM66 in osteosarcoma, TRIM68 in prostate). The altered expression of this TRIMs has been correlated with poor prognosis [50][51][52][53][54] (Table 1). On the contrary, there are also many TRIMs downregulated in tumors. TRIMs 3, 8, 13, 16, 21, 62 are downregulated in many of the main cancers worldwide (breast, gastric, liver, lung, osteosarcoma, prostate, kidney) [55][56][57][58][59][60][61][62][63][64][65][66], while some TRIMs are under-expressed in a cancer-specific way (e.g., TRIM15 in gastric cancer, TRIM26 in liver, TRIM58 in lung). In these cases, their downregulation is correlated with early-onset and poor overall survival among cancer patients [67][68][69] (Table 1).
Table 1. TRIM proteins in tumors. Tripartite motif (TRIM) proteins described in the manuscript are listed based on their expression levels in the main cancer types worldwide.
Cancer Type | Upregulated TRIMs | Downregulated TRIMs |
---|---|---|
Breast | 11 [47], 24 [12], 25 [8], 27 [10], 28 [9], 32 [42], 33 [70], 37 [17], 44 [32], 47 [48], 59 [39], 63 [54] |
8 [66], 13 [65], 16 [62], 21 [63], 62 [55] |
Gastric | 14 [71], 24 [19], 28 [11], 32 [31], 37 [41], 44 [14], 59 [40] |
3 [72], 15 [69] |
Liver | 11 [27], 14 [36], 24 [43], 28 [25], 31 [52], 32 [20], 35 [51], 37 [18], 65 [35] |
3 [56], 16 [60], 21 [58], 26 [67], 29 [73], 33 [74] |
Lung | 11 [44], 22 [33], 24 [15], 25 [23], 27 [13], 28 [16], 29 [75], 32 [46], 37 [37], 44 [26], 47 [28], 59 [29], 65 [24] |
13 [64], 16 [59], 58 [68], 62 [57] |
Osteosarcoma | 2 [76][77], 29 [78], 37 [34], 59 [22], 66 [53] |
8 [79] |
Prostate | 24 [45], 25 [80], 28 [38], 47 [21], 68 [50] |
16 [61], 29 [81] |
Renal | 44 [49], 59 [30] | 2 [82], 8 [83][84], 33 [85][86] |
Interestingly, there are some TRIM proteins, which result in being up- or down- regulated depending on cancer type. Among them are TRIM2 (up-regulated in osteosarcoma, down-regulated in kidney cancer), TRIM29 (up-regulated in lung cancer and osteosarcoma, down-regulated in liver and prostate cancers), TRIM33 (up-regulated in breast cancer, down-regulated in liver and kidney cancers) [74][81][85][70][75][86][82][76][77].
At the basis of the correlation between TRIMs, altered expression and tumor onset, there are, generally, several mechanisms, not fully understood, such as chromosomal translocations (resulting in oncogenic gain-of-function fusion genes), that likely contribute to oncogenesis through the constitutive activation of oncogenic signaling pathways, hyper- or hypo- methylation of CpG islands present in the TRIMs promoter regions [5][87][88][89][90][91]. Alternatively, the low expression of the tumor-suppressive TRIMs is inversely correlated with specific micro RNAs (miRs) overexpression (e.g., TRIM8 vs. miR17-92 family). On the contrary, overexpression of some oncogenic TRIMs in various cancers is frequently due to the loss of miR dependent gene suppression (e.g., TRIM11, TRIM14, TRIM24, TRIM25, and TRIM44) [71][83][92][93][94][95][96][97][98].
The pivotal role of TRIMs, in the pathological as well as in the physiological cellular life, is now clear if we consider that one or more TRIM members can influence diverse key downstream effector cellular pathways, such as p53 controlled pathways, the Wnt/β-catenin signaling, Transforming Growth Factor-β (TGF-β), Phosphoinositide-3-kinase /Protein Kinase B (PI3K/Akt) pathways and the pro-inflammatory Signal transducer and activator of transcription 3- Nuclear Factor kappa-light-chain-enhancer of activated B cells (STAT3-NF-κB) pathways.
Different TRIM proteins are involved in development and progression of CRC. They can regulate various aspects of tumorigenesis, including proliferation, apoptosis, autophagy, transcriptional regulation, chromatin remodeling, invasion, metastasis and chemoresistance [99]. Cancer cells, through different mechanisms such as inactivation of the tumor suppressor gene p53, may acquire resistance to chemotherapy. For this reason, the reactivation of wild type p53, through the TRIM proteins, could be a promising strategy to restore sensitivity to the treatment of chemotherapy in all tumors including CRC [100][101]. Below we describe the role and the levels of the different TRIMs in the CRC.
TRIM23 is upregulated in CRC, it binds p53, inducing its ubiquitination and promoting colorectal cell proliferation [80]; TRIM24 (transcription intermediary factor 1α-TIF1α), mRNA and protein levels were higher in CRC tissues compared to controls, indicating this TRIM is a potential negative prognostic marker. In particular, TRIM24 promotes the degradation of p53 via ubiquitination [102].
The literature reports that TRIM25 negatively regulates the expression of Caspase-2, and consequently the reduction of TRIM25 levels in the colorectal cell increases their sensibility to drugs [102]; moreover, TRIM25 reduction induces p53 acetylation and p53-dependent cell death in HCT116 cells [103][104][105]. This TRIM regulates p53 levels and activity in the HCT116 cell line in two opposite ways. From one side, TRIM25 prevents the formation of the ternary complex constituted by p53, MDM2, and p300, which is essential for p53-polyubiquitination and degradation, leading to the increase in p53 stability. Despite this, from another side, p53 transcriptional activity is inhibited in the presence of TRIM25, since the same p53-MDM2-p300 complex is required for p53 acetylation and, consequently, it is able to block the p53-dependent activation of p53-controlled apoptotic genes, following DNA damage [103].
TRIM59 is upregulated in CRC patients and correlates with a poor prognosis. Therefore, the reduction of TRIM59 levels reversed the expression of epithelial-mesenchymal transformation-related proteins vimentin, in p53 wild-type and p53 mutated cells, demonstrating that the TRIM59 oncogenic action is p53 independent [106][107]. In CRC, it has not been studied whether the oncogenic role of TRIM59 is through direct degradation of p53; only in stomach cancer does the literature report a direct TRIM59-p53 interaction and subsequent p53 degradation [108].
TRIM28 and TRIM29 are markers for patient survival in CRC. TRIM28 binds MDM2 and promotes the degradation of p53 [109]. In addition, TRIM28, in concert with MDM2, promotes the formation of a p53 complex with histone deacetylase 1 (HDAC1), thus preventing acetylation of p53 [110]. To date, it is unclear by which molecular mechanism TRIM29 regulates the development of CRC; in fact, this TRIM could prevent p53-mediated transcription of its target genes in the nucleus by sequestering p53 outside the nucleus and thus preventing its p300-dependent acetylation [111]. Alternatively, it could promote p53 degradation by degrading and/or changing the localization of TIP60, a transcriptional coactivator of p53, consequently reducing TIP60-dependent p53 acetylation [73]. In contrast, histone deacetylase9 (HDAC9) can inhibit the action of TRIM29, resulting in increased p53 activity and reduced cell survival [111].
Some TRIM proteins behave like oncogenes because they are involved in the activation of pro-proliferative pathways such as Akt/mTOR and NF-κB signaling pathways. In particular, TRIM2 and TRIM47 are potential targets for therapy in CRC, since they promote cell proliferation, epithelial-mesenchymal transition (EMT) and metastasis in vitro and in vivo [77][112]. TRIM6 is upregulated in CRC and its reduction increases the anti-proliferative effects of 5-fluorouracil and oxaliplatin [113]. TRIM27 and TRIM44 are involved in activation of the Akt/mTOR signaling pathway inducing cell proliferation, migration, invasion and metastasis in CRC [114][115]. Additionally, TRIM66, TRIM52 and TRIM14 also play an oncogenic role in CRC, since they are involved in cancer proliferation and metastasis through the regulation of STAT3 pathway expression [53][71][116][117]. Instead, TRIM27 is involved in proliferation, invasion and metastasis of CRC in vitro and in vivo regulating AKT [114]. TRIM14, together with TRIM1, have a role in autophagy. Indeed, TRIM14 negatively interferes with the autophagic degradation of the NF-κB family member p100/p52, inducing a non-canonical NF-κB signaling pathway [118]. By contrast, TRIM11 mediates the degradation of the receptor-interacting protein kinase 3 (RIPK3). RIPK3 activation is linked to necrotic cell death and represents a causative role for both pediatric and adult IBDs (inflammatory bowel diseases). TRIM11 counteracts mTOR-induced activation of RIPK3, inducing RIPK3 degradation through autophagy and thus representing a novel regulatory mechanism important for antagonizing necroptosis [119]. In this way, TRIM11 shows a protective role in the gut, mainly through antagonizing intestinal inflammation and cancer.
Finally, TRIM31 and TRIM40 interfere with the canonical NF–κB pathway, promoting invasion and metastasis in CRC [120][118]. In particular, TRIM40 is downregulated in gastrointestinal cancers. It is able to inhibit the NF-κB activity by promoting the neddylation of the IKKγ, also called NEMO (NF–κB essential modulator), a key regulator for NF-κB activation, thus preventing inflammation-associated carcinogenesis in the GI tract [121]. In contrast to the oncogenic action of the TRIMs described so far, TRIM67, TRIM58 and TRIM8 are downregulated in CRC, playing a tumor suppressor role. The reduction of TRIM67 levels in CRC is caused by methylation of two loci (cg21178978 and cg27504802). Mechanistically, TRIM67 binds p53, thus inhibiting MDM2 binding to p53 and following ubiquitination [122]. TRIM58 plays a critical role of tumor suppressor by limiting Wnt/β-catenin dependent EMT; indeed, the recovery of TRIM58 reduces tumor invasion [123]. TRIM8 seems to be down-regulated in CRC and in restoring TRIM8 levels, p53 is stabilized, and cells become sensitive again to chemotherapeutics (The Human protein Atlas, available from http://www.proteinatlas.org, accessed on 25 February 2021) [84][124][99][125].