Negative Regulation of Serine Threonine Kinase 11 (STK11) through miR-100 in Head and Neck Cancer

BACKGROUND

Serine Threonine Kinase 11 (STK11), also known as LKB1, is a tumor suppressor gene that regulates several biological processes such as apoptosis, energetic metabolism, proliferation, invasion, and migration. During malignant progression, different types of cancer inhibit STK11 function by mutation or epigenetic inactivation. In Head and Neck Cancer, it is unclear what mechanism is involved in decreasing STK11 levels. Thus, the present work aims to determine whether STK11 expression might be regulated through epigenetic or post-translational mechanisms.

METHODS

Expression levels and methylation status for STK11 were analyzed in 59 cases of head and neck cancer and 10 healthy tissue counterparts. Afterward, we sought to identify candidate miRNAs exerting post-transcriptional regulation of STK11. Then, we assessed a luciferase gene reporter assay to know if miRNAs directly target STK11 mRNA. The expression levels of the clinical significance of mir-100-3p, -5p, and STK11 in 495 HNC specimens obtained from the TCGA database were further analyzed. Finally, the Kaplan-Meier method was used to estimate the prognostic significance of the miRNAs for Overall Survival, and survival curves were compared through the log-rank test.

RESULTS

STK11 was under-expressed, and its promoter region was demethylated or partially methylated. miR-17-5p, miR-106a-5p, miR-100-3p, and miR-100-5p could be negative regulators of STK11. Our experimental data suggested evidence that miR-100-3p and -5p were over-expressed in analyzed tumor patient samples. Luciferase gene reporter assay experiments showed that miR-100-3p targets and down-regulates STK11 mRNA directly. With respect to overall survival, STK11 expression level was significant for predicting clinical outcomes.

CONCLUSION

This is, to our knowledge, the first report of miR-100-3p targeting STK11 in HNC. Together, these findings may support the importance of regulation of STK11 through post-transcriptional regulation in HNC and the possible contribution to the carcinogenesis process in this neoplasia.

[Expression of cathepsin D in breast cancer and its clinical and histopathological correlations]

BACKGROUND

Cathepsin D is a lysosomal protease which is overexpressed in some cases of breast cancer. Several studies done in tumor cytosol have shown that high levels of cathepsin D are associated with poor prognosis in patients with breast cancer but the results are not conclusive using immunohistochemistry methods to assay cathepsin D.

OBJECTIVE

To evaluate if cathepsin D, assayed by a immunohistochemical technique using a polyclonal antibody, can be considered an independent prognostic factor in breast cancer.

PATIENTS AND METHODS

Paraffine embedded sections of 68 tumor specimens from breast cancer patients in stages I to IV seen at the Instituto Nacional de Cancerologia during the period from 1985 to 1986.

RESULTS

From the 68 patients, 35 (51%) had an intense positive staining for cathepsin D, 19 (28%) han mild staining and 14 (21%) were negative. Ten patients with mild staining had artifacts due to deficiencies in the tissue fixation technique. Cathepsin D expression did not have a prognostic value nor association with other clinical and histopathological prognostic factors well established in breast cancer.

CONCLUSION

Cathepsin D determined by immunohistochemistry has no prognostic value in breast cancer.