The Initiator Methionine tRNA Drives Secretion of Type II Collagen from Stromal Fibroblasts to Promote Tumor Growth and Angiogenesis

Abstract

SummaryExpression of the initiator methionine tRNA (tRNAiMet) is deregulated in cancer. Despite this fact, it is not currently known how tRNAiMet expression levels influence tumor progression. We have found that tRNAiMet expression is increased in carcinoma-associated fibroblasts, implicating deregulated expression of tRNAiMet in the tumor stroma as a possible contributor to tumor progression. To investigate how elevated stromal tRNAiMet contributes to tumor progression, we generated a mouse expressing additional copies of the tRNAiMet gene (2+tRNAiMet mouse). Growth and vascularization of subcutaneous tumor allografts was enhanced in 2+tRNAiMet mice compared with wild-type littermate controls. Extracellular matrix (ECM) deposited by fibroblasts from 2+tRNAiMet mice supported enhanced endothelial cell and fibroblast migration. SILAC mass spectrometry indicated that elevated expression of tRNAiMet significantly increased synthesis and secretion of certain types of collagen, in particular type II collagen. Suppression of type II collagen opposed the ability of tRNAiMet-overexpressing fibroblasts to deposit pro-migratory ECM. We used the prolyl hydroxylase inhibitor ethyl-3,4-dihydroxybenzoate (DHB) to determine whether collagen synthesis contributes to the tRNAiMet-driven pro-tumorigenic stroma in vivo. DHB had no effect on the growth of syngeneic allografts in wild-type mice but opposed the ability of 2+tRNAiMet mice to support increased angiogenesis and tumor growth. Finally, collagen II expression predicts poor prognosis in high-grade serous ovarian carcinoma. Taken together, these data indicate that increased tRNAiMet levels contribute to tumor progression by enhancing the ability of stromal fibroblasts to synthesize and secrete a type II collagen-rich ECM that supports endothelial cell migration and angiogenesis.

The initiator methionine tRNA drives cell migration and invasion leading to increased metastatic potential in melanoma

“…As we have previously shown that elevated tRNA i Met levels do not lead to upregulated protein synthesis, increased cell proliferation (Clarke et al, 2016), or altered energy metabolism (data not shown) we looked at the ability of this tRNA to influence other cell characteristics that are associated with cancer aggressiveness. Initially we compared the migratory behaviour of immortalised mouse embryonic fibroblasts (iMEFs), which overexpress tRNA i Met (iMEF.tRNA i Met ), with those expressing an empty vector as control (iMEF.Vector).…”

“…Thus it would seem natural to propose that this alteration to the tRNA repertoire would drive increased use of the AUG codon leading to upregulation of translation initiation and protein synthesis to support cancer cell growth and proliferation. However, a recent study in stromal fibroblasts indicate that elevated levels of tRNA i Met do not directly support increased cellular protein synthesis and proliferation (Clarke et al, 2016). Rather, increased tRNA i Met alters the fibroblast secretome to favour synthesis and secretion of certain collagens (particularly type II collagen) which are incorporated into the tumour extracellular matrix (ECM).…”

“…Because Pol III products are thought to be increased in tumour cells (White, 2005) as well as in stromal fibroblasts (Clarke et al, 2016), we have generated approaches to manipulate levels of Pol III and its product tRNA i Met in tumour cells and have determined the consequences of this on tumour cell behaviour. Using both in vitro and in vivo approaches we show that increased levels of tRNA i Met in tumour cells drives metastasis by enlisting integrin-dependent cell migration and invasion without influencing cell growth or proliferation, indicating that the cell migratory machinery responds to alterations in the tRNA repertoire during the metastatic process.…”

tRNA-Derived Fragments as Novel Predictive Biomarkers for Trastuzumab-Resistant Breast Cancer

“…Several studies have indicated that tRNAs play roles in modulating cell proliferation and cancer progression [15][16][17]. tRNA halves (tRHs) and tRNA-derived small RNA fragments (tRFs) belong to a novel class of sncRNAs that are generated through precise cleavage of tRNAs [18][19][20].…”

tRNA biology in the omics era: Stress signalling dynamics and cancer progression

“…These phenotypes are mimicked by overexpression of the initiator methionine tRNA (tRNA i Met ), which is responsible for the selection of the correct start codon during translation initiation. In human breast epithelial cells, overexpression of tRNA i Met promotes increased metabolic activity and proliferation [66] and, in a recent study, a transgenic mouse carrying two extra copies of the tRNA i Met gene showed enhanced tumor growth and vascularisation [67]. The latter was mainly due to tRNA i Met -dependent secretion of type II collagen by stromal fibroblasts, which in turn promoted angiogenesis and was generally associated with the aggressiveness of primary ovarian tumors.…”