Telomere length alterations in microsatellite stable colorectal cancer and association with the immune response

Role of telomere length in human carcinogenesis (Review)

Cancer is considered the most important clinical, social and economic issue regarding cause‑specific disability‑adjusted life years among all human pathologies. Exogenous, endogenous and individual factors, including genetic predisposition, participate in cancer triggering. Telomeres are specific DNA structures positioned at the end of chromosomes and consist of repetitive nucleotide sequences, which, together with shelterin proteins, facilitate the maintenance of chromosome stability, while protecting them from genomic erosion. Even though the connection between telomere status and carcinogenesis has been identified, the absence of a universal or even a cancer‑specific trend renders consent even more complex. It is indicative that both short and long telomere lengths have been associated with a high risk of cancer incidence. When evaluating risk associations between cancer and telomere length, a disparity appears to emerge. Even though shorter telomeres have been adopted as a marker of poorer health status and an older biological age, longer telomeres due to increased cell growth potential are associated with the acquirement of cancer‑initiating somatic mutations. Therefore, the present review aimed to comprehensively present the multifaceted pattern of telomere length and cancer incidence association.

The dynamics of telomere length in primary and metastatic colorectal cancer lesions

Telomeric sequences, the structures comprised of hexanucleotide repeats and associated proteins, play a pivotal role in chromosome end protection and preservation of genomic stability. Herein we address telomere length (TL) dynamics in primary colorectal cancer (CRC) tumour tissues and corresponding liver metastases. TL was measured by multiplex monochrome real-time qPCR in paired samples of primary tumours and liver metastases along with non-cancerous reference tissues obtained from 51 patients diagnosed with metastatic CRC. Telomere shortening was observed in the majority of primary tumour tissues compared to non-cancerous mucosa (84.1%, p < 0.0001). Tumours located within the proximal colon had shorter TL than those in the rectum (p < 0.05). TL in liver metastases was not significantly different from that in primary tumours (p = 0.41). TL in metastatic tissue was shorter in the patients diagnosed with metachronous liver metastases than in those diagnosed with synchronous liver metastases (p = 0.03). The metastatic liver lesions size correlated with the TL in metastases (p < 0.05). Following the neoadjuvant treatment, the patients with rectal cancer had shortened telomeres in tumour tissue than prior to the therapy (p = 0.01). Patients with a TL ratio between tumour tissue and the adjacent non-cancerous mucosa of ≥ 0.387 were associated with increased overall survival (p = 0.01). This study provides insights into TL dynamics during progression of the disease. The results show TL differences in metastatic lesions and may help in clinical practice to predict the patient's prognosis.

Relative Telomere Length Change in Colorectal Carcinoma and Its Association with Tumor Characteristics, Gene Expression and Microsatellite Instability

We compared tumor and adjacent normal tissue samples from 165 colorectal carcinoma (CRC) patients to study change in relative telomere length (RTL) and its association with different histological and molecular features. To measure RTL, we used a Luminex-based assay. We observed shorter RTL in the CRC tissue compared to paired normal tissue (RTL 0.722 ± SD 0.277 vs. 0.809 ± SD 0.242, p = 0.00012). This magnitude of RTL shortening (by ~0.08) in tumor tissue is equivalent to RTL shortening seen in human leukocytes over 10 years of aging measured by the same assay. RTL was shorter in cancer tissue, irrespective of age group, gender, tumor pathology, location and microsatellite instability (MSI) status. RTL shortening was more prominent in low-grade CRC and in the presence of microsatellite instability (MSI). In a subset of patients, we also examined differential gene expression of (a) telomere-related genes, (b) genes in selected cancer-related pathways and (c) genes at the genome-wide level in CRC tissues to determine the association between gene expression and RTL changes. RTL shortening in CRC was associated with (a) upregulation of DNA replication genes, cyclin dependent-kinase genes (anti-tumor suppressor) and (b) downregulation of "caspase executor", reducing apoptosis.

Long noncoding RNA: A resident staff of genomic instability regulation in tumorigenesis

Genomic instability is an important characteristic of cancer, which promotes clonal evolution and tumorigenesis by increasing the frequency of gene destruction and loss of genome integrity. Generally, the maintenance of genomic stability depends significantly on the accurate regulation and timely repair of different genomic scales, ranging from DNA sequence to chromatin higher-order structures to chromosomes. Once irreversible damage and imperfect repair occurred, the resulting genomic instability can lead to a higher risk of tumorigenesis. However, how these factors disrupt genomic stability and their specific tumorigenic mechanisms remain unclear. Inspiringly, numerous studies have confirmed that long noncoding RNAs (lncRNAs), an important regulator of epigenetic inheritance, are functional in such process. Thus, this review aimed to discuss the vital factors that may lead to genomic instability at these multiple genomic scales, with an emphasis on the role of lncRNAs in it.

Identification of prognosis-related genes in the cervical cancer immune microenvironment

BACKGROUND

Cervical cancer is the fourth most commonly diagnosed cancer in women worldwide. The metastasis and invasion of this type of cancer are closely related to the tumor microenvironment. Immune cells and stromal cells dominate the tumor microenvironment in cervical cancer. Therefore, we should further investigate the complex interplay between the tumor progression with immune cells or stromal cells.

METHODS

We downloaded the gene expression profiles and clinical data of 307 patients with cervical cancers based on the TCGA database. Subsequently, the Estimation of Stromal and Immune cells in Malignant Tumours using Expression data (ESTIMATE) algorithm was used to calculate the scores of stromal cells and immune cells in order to uncover differential expressed genes, and we analyzed the correlation between their scores and patient survival. Then the Cell type Identification By Estimating Relative Subsets Of known RNA Transcripts (CIBERSORT) deconvolution algorithm was applied to quantify the fraction and infiltration of 22 types of immune cells in cervical cancer. Moreover, we also used R language packs and network tools to analyze GO term, gene enrichment pathway, and protein-protein relationship to trace down genes related to inflammation and immune regulation.

RESULTS

The gene expression profiles and corresponding clinical data of 307 patients were obtained from TCGA database. The results showed that the scores were statistically significant between the high immunescore group and the low immunescore group. And the low immunescore group had shorter survival period than the high scores group (P = 0.035). Among the 22 types of immune cells, only T cells and mast cells were significantly related to the survival rate of cervical cancer patients. Moreover, PPI network analysis revealed that CCR5 and CXCL9, -10, -11/CXCR3 axis might be a new target for cervical cancer treatment. Finally, Kaplan-Meier survival curves found outnine representative genes significantly related to survival rate including BTNL8, CCR7, CD1E, CD6, CD27, CD79A, GRAP2, SP1B, LY9.

CONCLUSIONS

These genes can be used as markers for the prognosis and diagnosis of cervical cancer and also might be used as treatment targets.