Knockdown of TRIM35 suppresses cell proliferation and metastasis by modulating the PPAR signalling pathway in papillary thyroid cancer cells.

Background: Although patients with papillary thyroid cancer (PTC) generally have a favourable prognosis, they still face the possibility of recurrence after surgery. Identifying biomarkers related to PTC initiation and progression is crucial. The role and regulatory mechanisms of tripartite motif containing 35 (TRIM35) in PTC remain unclear. This study aimed to investigate the expression, biological functions, and underlying mechanisms of TRIM35 in PTC. Methods: The expression of TRIM35 was evaluated via immunohistochemistry, and its association with patient clinicopathological features was examined with Fisher's exact test. In PTC cell lines, TRIM35 was silenced using small interfering RNA (siRNA). A series of functional assays were then performed. Cell viability was measured with the Cell Counting Kit-8. Cell motility was assessed via wound healing assays. Cell migration and invasion were evaluated using Transwell chambers, with invasion assays specifically employing a Matrigel coating. Commercial assay kits were employed to quantify lactate production along with the expression of key glycolytic enzymes-hexokinase (HK) and lactate dehydrogenase A (LDHA). Transcriptomic sequencing was conducted to identify differentially expressed genes (DEGs) in TRIM35-knockdown K1 cells. Finally, protein levels of peroxisome proliferator-activated receptor gamma (PPARγ) and cluster of differentiation 36 (CD36) were detected by western blot analysis. Results: TRIM35 expression was elevated in cancerous tissues, and its levels were closely linked to tumour size and the presence of lymphovascular invasion. Knockdown of TRIM35 notably suppressed cellular growth and metastasis of PTC cells. Interestingly, PTC cells with reduced TRIM35 levels produced significantly lower amounts of lactate. Moreover, we detected a notable decrease in the levels of HK and LDHA, in TRIM35-knockdown K1 and TPC-1 cells. Seventy-five downregulated and 103 upregulated DEGs were identified in TRIM35-knockdown cells. PPAR signalling pathway was enriched in the top 20 enriched Kyoto Encyclopedia of Genes and Genomes pathways. TRIM35 knockdown significantly suppressed the expression of both PPAR γ and CD36. Conclusions: Elevated TRIM35 expression was associated with larger tumour size and the presence of lymphovascular invasion. Functionally, TRIM35 drives malignant phenotypes and glycolytic metabolism in PTC cells, likely via the PPAR pathway. Our present study indicates that TRIM35 may serve as a promising biomarker indicative of PTC progression.