LncRNA <i>GAS8-AS1</i> is downregulated, correlates with early-stage disease and lymph node metastasis, and its knockdown promotes proliferation, migration, and invasion in differentiated thyroid cancer

<h4>Background</h4>LncRNAs emerge as critical regulators of gene expression and epigenetic modulation in human cancer. However, the biological and clinical significance of the lncRNA <i>GAS8-AS1</i> in differentiated thyroid cancers (DTCs) remains poorly understood.<h4>Methods</h4><i>GAS8-AS1</i> expression in normal tissues was evaluated using LncExpDB. Quantitative RT-PCR was performed on 21 DTCs with matched adjacent normal tissues. RNA-seq data from TCGA (507 DTCs) were analyzed to assess <i>GAS8-AS1</i> expression and clinicopathological associations. Independent validation was conducted using ENCORI (510 thyroid cancer, 58 normal) and TNMplot datasets. Expression profiles of <i>GAS8-AS1</i>-associated genes were analyzed in TCGA and were corroborated with ENCORI dataset. Co-expression analyses were performed to identify regulatory relationships. Functional characterization was conducted using siRNA-mediated knockdown of <i>GAS8-AS1</i> in HEK293T and BCPAP cells, and overexpression studies in papillary thyroid cancer cell lines (K1 and BCPAP). Cell proliferation, migration, and invasion assays were performed. Pathway enrichment analyses were used to identify <i>GAS8-AS1</i>-mediated biological processes.<h4>Results</h4><i>GAS8-AS1</i> expression was significantly downregulated in DTCs compared with matched normal tissues (<i>p</i> < 0.0001). TCGA analysis confirmed lower <i>GAS8-AS1</i> expression, which was markedly associated with early-stage disease (<i>p</i> = 0.03) and lymph node metastasis (<i>p</i> = 0.03). <i>GAS8-AS1</i> downregulation was remarkably consistent in thyroid cancer (ENCORI, <i>p</i> = 0.004). A dramatic downregulation of <i>GAS8-AS1</i> was also observed across pan-cancer, including thyroid cancer (TNMplot, <i>p</i> = 2.01 × 10^-128). Expression analysis of <i>GAS8-AS1</i>-associated genes revealed frequent deregulation in DTCs (24%), including downregulation of <i>ATF2, ATG5, ATG7</i>, and <i>BECN1</i>, and upregulation of <i>NEAT1</i> and <i>UCA1</i>. Co-expression analysis revealed that <i>GAS8-AS1</i> and <i>ATG5</i> expression levels were positively correlated with <i>ATF2</i>, whereas <i>NEAT1</i> showed a negative association, suggesting <i>ATF2</i>-dependent transcriptional regulation of <i>GAS8-AS1</i>, <i>ATG5</i>, and <i>NEAT1</i>. Functional characterizations demonstrated that <i>GAS8-AS1</i> knockdown significantly increased proliferation, migration, and invasion, whereas <i>GAS8-AS1</i> overexpression markedly suppressed tumor cell proliferation. Pathway enrichment analyses implicated <i>GAS8-AS1</i>-related genes in autophagy, apoptosis, proliferation, invasion, and metastasis.<h4>Conclusion</h4>These findings demonstrate that <i>GAS8-AS1</i> may function as a tumor suppressor in DTCs, with its downregulation associated with disease progression and metastasis. The consistent loss of <i>GAS8-AS1</i> expression and its functional impact on tumor progression suggest that it may serve as a valuable diagnostic and prognostic biomarker in DTCs.