Synergistic activation of mutant TERT promoter by Sp1 and GABPA in BRAF(V600E)-driven human cancers

Risk stratification for radioactive iodine refractoriness using molecular alterations in distant metastatic differentiated thyroid cancer

Objective

Patients with radioactive iodine-refractory differentiated thyroid cancer (RAIR-DTC) are often diagnosed with delay and constrained to limited treatment options. The correlation between RAI refractoriness and the underlying genetic characteristics has not been extensively studied.

Methods

Adult patients with distant metastatic DTC were enrolled and assigned to undergo next-generation sequencing of a customized 26-gene panel (ThyroLead). Patients were classified into RAIR-DTC or non-RAIR groups to determine the differences in clinicopathological and molecular characteristics. Molecular risk stratification (MRS) was constructed based on the association between molecular alterations identified and RAI refractoriness, and the results were classified as high, intermediate or low MRS.

Results

A total of 220 patients with distant metastases were included, 63.2% of whom were identified as RAIR-DTC. Genetic alterations were identified in 90% of all the patients, with BRAF (59.7% vs. 17.3%), TERT promoter (43.9% vs. 7.4%), and TP53 mutations (11.5% vs. 3.7%) being more prevalent in the RAIR-DTC group than in the non-RAIR group, except for RET fusions (15.8% vs. 39.5%), which had the opposite pattern. BRAF and TERT promoter are independent predictors of RAIR-DTC, accounting for 67.6% of patients with RAIR-DTC. MRS was strongly associated with RAI refractoriness (P<0.001), with an odds ratio (OR) of high to low MRS of 7.52 [95% confidence interval (95% CI), 3.96-14.28; P<0.001] and an OR of intermediate to low MRS of 3.20 (95% CI, 1.01-10.14; P=0.041).

Conclusions

Molecular alterations were associated with RAI refractoriness, with BRAF and TERT promoter mutations being the predominant contributors, followed by TP53 and DICER1 mutations. MRS might serve as a valuable tool for both prognosticating clinical outcomes and directing precision-based therapeutic interventions.

The regulations of telomerase reverse transcriptase (TERT) in cancer

Abnormal activation of telomerase occurs in most cancer types, which facilitates escaping from cell senescence. As the key component of telomerase, telomerase reverse transcriptase (TERT) is regulated by various regulation pathways. TERT gene changing in its promoter and phosphorylation respectively leads to TERT ectopic expression at the transcription and protein levels. The co-interacting factors play an important role in the regulation of TERT in different cancer types. In this review, we focus on the regulators of TERT and these downstream functions in cancer regulation. Determining the specific regulatory mechanism will help to facilitate the development of a cancer treatment strategy that targets telomerase and cancer cell senescence. As the most important catalytic subunit component of telomerase, TERT is rapidly regulated by transcriptional factors and PTM-related activation. These changes directly influence TERT-related telomere maintenance by regulating telomerase activity in telomerase-positive cancer cells, telomerase assembly with telomere-binding proteins, and recruiting telomerase to the telomere. Besides, there are also non-canonical functions that are influenced by TERT, including the basic biological functions of cancer cells, such as proliferation, apoptosis, cell cycle regulation, initiating cell formation, EMT, and cell invasion. Other downstream effects are the results of the influence of transcriptional factors by TERT. Currently, some small molecular inhibitors of TERT and TERT vaccine are under research as a clinical therapeutic target. Purposeful work is in progress.

Interrogation of TERT promoter hotspot mutations in ameloblastoma and ameloblastic carcinoma

BACKGROUND

TERT promoter mutations increase telomerase activity, conferring cell immortality. The coexistence of TERT promoter mutations with BRAFV600E is associated with aggressiveness. Ameloblastoma and ameloblastic carcinoma are infiltrative neoplasms that harbor BRAFV600E; however, it remains unknown if these odontogenic tumors also show TERT promoter mutations.

METHODS

Genomic DNA of paraffin-embedded ameloblastomas (n = 6) and ameloblastic carcinomas (n = 3) were Sanger-sequenced to assess the hotspot TERT promoter mutations C228T and C250T. BRAFV600E status was screened by TaqMan allele-specific quantitative polymerase chain reaction.

RESULTS

None of the samples harbored TERT promoter mutations. The BRAFV600E mutation was positive in 3 of 6 of ameloblastomas and in 1 of 3 of ameloblastic carcinomas.

CONCLUSION

The absence of TERT promoter mutation in the samples indicates that this molecular event is not relevant to the tumors' pathogenesis. Further studies are necessary to explore undefined genetic or epigenetic mechanisms related to TERT-upregulation in ameloblastoma, and the telomerase activity in ameloblastic carcinoma.

Sorafenib decreases glycemia by impairing hepatic glucose metabolism

PURPOSE

Sorafenib has been reported to reduce blood glucose levels in diabetic and non-diabetic patients in previous retrospective studies. However, the mechanism of which the hypoglycemic effects of sorafenib is not clearly explored. In this study, we investigated the effect of sorafenib on blood glucose levels in diabetic and normal mice and explored the possible mechanism.

METHODS

We established a mouse model of type 2 diabetes by a high-fat diet combined with a low-dose of streptozotocin (STZ), to identify the hypoglycemic effect of sorafenib in different mice. Glucose tolerance, insulin tolerance and pyruvate tolerance tests were done after daily gavage with sorafenib to diabetic and control mice. To explore the molecular mechanism by which sorafenib regulates blood glucose levels, hepatic glucose metabolism signaling was studied by a series of in vivo and in vitro experiments.

RESULTS

Sorafenib reduced blood glucose levels in both control and diabetic mice, particularly in the latter. The diabetic mice exhibited improved glucose and insulin tolerance after sorafenib treatment. Further studies showed that the expressions of gluconeogenesis-related enzymes, such as PCK1, G6PC and PCB, were significantly decreased upon sorafenib treatment. Mechanistically, sorafenib downregulates the expression of c-MYC downstream targets PCK1, G6PC and PCB through blocking the ERK/c-MYC signaling pathway, thereby playing its hypoglycemic effect by impairing hepatic glucose metabolism.

CONCLUSION

Sorafenib reduces blood glucose levels through downregulating gluconeogenic genes, especially in diabetic mice, suggesting the patients with T2DM when treated with sorafenib need more emphasis in monitoring blood glucose to avoid unnecessary hypoglycemia.

Occurrence, functionality and abundance of the TERT promoter mutations

Telomere shortening at chromosomal ends due to the constraints of the DNA replication process acts as a tumor suppressor by restricting the replicative potential in primary cells. Cancers evade that limitation primarily through the reactivation of telomerase via different mechanisms. Mutations within the promoter of the telomerase reverse transcriptase (TERT) gene represent a definite mechanism for the ribonucleic enzyme regeneration predominantly in cancers that arise from tissues with low rates of self-renewal. The promoter mutations cause a moderate increase in TERT transcription and consequent telomerase upregulation to the levels sufficient to delay replicative senescence but not prevent bulk telomere shortening and genomic instability. Since the discovery, a staggering number of studies have resolved the discrete aspects, effects and clinical relevance of the TERT promoter mutations. The promoter mutations link transcription of TERT with oncogenic pathways, associate with markers of poor outcome and define patients with reduced survivals in several cancers. In this review, we discuss the occurrence and impact of the promoter mutations and highlight the mechanism of TERT activation. We further deliberate on the foundational question of the abundance of the TERT promoter mutations and a general dearth of functional mutations within noncoding sequences, as evident from pan-cancer analysis of the whole-genomes. We posit that the favorable genomic constellation within the TERT promoter may be less than a common occurrence in other noncoding functional elements. Besides, the evolutionary constraints limit the functional fraction within the human genome, hence the lack of abundant mutations outside the coding sequences.

Synergistic activation of mutant TERT promoter by Sp1 and GABPA in BRAFV600E-driven human cancers

The activating TERT promoter mutations and BRAF^V600E mutation are well-established oncogenic alterations in human cancers. Coexistence of BRAF^V600E and TERT promoter mutations is frequently found in multiple cancer types, and is strongly associated with poor patient prognosis. Although the BRAF^V600E-elicited activation of ERK has been demonstrated to contribute to TERT reactivation by maintaining an active chromatin state, it still remains to be addressed how activated ERK is selectively recruited to mutant TERT promoter. Here, we report that transcription factor GABPA mediates the regulation of BRAF^V600E/MAPK signaling on TERT reactivation by selectively recruiting activated ERK to mutant TERT promoter, where activated ERK can phosphorylate Sp1, thereby resulting in HDAC1 dissociation and an active chromatin state. Meanwhile, phosphorylated Sp1 further enhances the binding of GABPA to mutant TERT promoter. Taken together, our data indicate that GABPA and Sp1 synergistically activate mutant TERT promoter, contributing to tumorigenesis and cancer progression, particularly in the BRAF^V600E-driven human cancers. Thus, our findings identify a direct mechanism that bridges two frequent oncogenic alterations together in TERT reactivation.