Mutational and expressional analysis of a haploinsufficient tumor suppressor gene DOK2 in gastric and colorectal cancers

Comprehensive analysis of DOK family genes expression, immune characteristics, and drug sensitivity in human tumors

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The expression of DOK family genes is related to overall survival (OS), clinical stage, tumor mutation, methylation, CNV, and SNV.

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DOK family genes are significantly associated with poor prognosis of UVM.

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DOK1-DOK3 has obvious correlation with tumor immunity and tumor microenvironment.

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DOK family gene is significantly related to tumor stemness and drug sensitivity.

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The expression of DOK family genes is related to the activation of EMT and hormone ER pathways, and is related to the inhibition of DNA damage response, cell cycle, and hormone AR pathways.

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DOK1 and DOK3, DOK2 and DOK3 have the significant correlation.

Introduction

Objectives

Methods

Results

Conclusions

DOK7V1 influences the malignant phenotype of lung cancer cells through PI3K/AKT/mTOR and FAK/paxillin signaling pathways

Downstream of tyrosine kinase 7 transcript variant 1 (DOK7V1) is a docking protein mediating signal transduction between receptors and intracellular downstream molecules. Our previous study indicated that DOK7V1 was decreased in lung cancer and its lower expression was associated with a decreased survival rate. The 5‑year overall survival rate for patients with lung cancer was 20.2 and 18.6% for high and low DOK7 expression, respectively; the 5‑year disease‑free survival rate for patients with lung cancer was 14.3 and 16.9% for high and low DOK7 expression, respectively. DOK7V1 inhibited proliferation and migration, but enhanced adhesion, of lung cancer cells. In the present study, the effect of DOK7V1 and its domains [pleckstrin homology (PH) and phosphotyrosine‑binding (PTB) domain] on the malignant phenotype and associated signaling pathway in lung cancer cells was investigated. The results indicated that truncation of DOK7V1 domains (DOK7V1Δ‑PH and DOK7V1Δ‑PTB) inhibited the proliferation and migration of lung cancer cells which exhibited the same trend as DOK7V1, whereas DOK7V1Δ‑PH and DOK7V1Δ‑PTB exhibited different functions from those of DOK7V1 in cell matrix adhesion. Consistently, DOK7V1 overexpression in lung cancer cells suppressed the phosphoinositide 3‑kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathways, but activated the focal adhesion kinase (FAK)/paxillin signaling pathway. Taken together, these results indicate that DOK7V1 may inhibit proliferation and migration via negatively regulating the PI3K/AKT/mTOR signaling pathway, and increase adhesion by upregulating the FAK/paxillin signaling pathway in lung cancer cells.

Co-expression and significance of Dok2 and Ras p21 protein activator 1 in breast cancer

Docking protein 2 (Dok2) and Ras p21 protein activator 1 (RASA1) are tumor suppressors which have been identified in numerous solid tumors; however, the association between their expression in breast cancer and patient prognosis remains unclear. A total of 285 consecutive patients diagnosed histopathologically with breast cancer who underwent surgery at Jingzhou Central Hospital were selected for the present study. Dok2 and RASA1 protein were explored using histopathology and western blotting techniques, and the association of patient prognosis with clinicopathological parameters was investigated using univariate and multivariate analyses. Weak expression of Dok2/RASA1 was associated with poorly differentiated breast adenocarcinomas; negatively expressed Dok2 and RASA1 were associated with increased tumor size, a higher proportion of axillary lymph node metastasis and later clinical staging. Additionally, Dok2 and RASA1 expression were associated with disease-free survival of patients with breast cancer. As indicated by Cox's regression analysis, Dok2 and RASA1 expression and the high proportion of axillary lymph node metastasis served as significant independent predictors for the recurrence of breast cancer. The results of the present study suggested that combined Dok2 and RASA1 negative expression may serve as an independent prognostic factor for patients following breast cancer surgery.

The downstream of tyrosine kinase 7 is reduced in lung cancer and is associated with poor survival of patients with lung cancer

The downstream of tyrosine kinase 7 (DOK7) is an adaptor protein mediating signalling transduction between receptors and intracellular downstream molecules. Reduced expression of DOK7 has been observed in breast cancer. The present study aimed to investigate the role played by DOK7 in lung cancer. The expression of DOK7 at both mRNA and protein levels was evaluated in human lung cancer. A reduced expression of DOK7 transcripts was seen in lung cancers compared with normal lung tissues. Kaplan-Meier analyses showed that the reduced expression of DOK7 was associated with poorer overall survival and progression-free survival of patients with lung cancer. A further western blot analysis revealed a predominant expression of DOK7 isoform 1 (DOK7V1) in normal lung tissues, which was reduced in lung cancer. Forced overexpression of DOK7V1 in lung cancer cell lines, A549 and H3122 resulted in a decrease of in vitro cell proliferation and migration, while adhesion to extracellular matrix was enhanced following the expression. In conclusion, DOK7 was reduced in lung cancer and reduced DOK7 expression was associated with poorer survival. DOK7 isoform 1 plays an inhibitory role on the proliferation and migration of lung cancer cells in which Akt pathway may be involved.

mRNA expression of DOK1-6 in human breast cancer

AIM: To examine the expression of downstream of tyrosine kinase (DOK)1-6 genes in normal and breast cancer tissue and correlated this with several clinico-pathological and prognostic factors.

METHODS: DOK1-6 mRNA extraction and reverse transcription were performed on fresh frozen breast cancer tissue samples (n = 112) and normal background breast tissue (n = 31). Tissues were collected between 1991 and 1996 at two centres and all patients underwent mastectomy and ipsilateral axillary node dissection. All tissues were randomly numbered and the details were only made known after all analyses were completed. Transcript levels of expression were determined using real-time polymerase chain reaction and analyzed against TNM stage, tumour grade and clinical outcome over a 10-year follow-up period.

RESULTS: DOK-2 and DOK-6 expression decreased with increasing TNM stage. DOK-6 expression decreased with increasing Nottingham Prognostic Index (NPI) [NPI-1 vs NPI-3 (mean copy number 15.4 vs 0.22, 95%CI: 2.7-27.6, P = 0.018) and NPI-2 vs NPI-3 (mean copy number 7.6 vs 0.22, 95%CI: 0.1-14.6, P = 0.048)]. After a median follow up period of 10 years, higher levels of DOK-2 expression were found among patients who remained disease-free compared to those who developed local or distant recurrence (mean copy number 3.94 vs 0.0000096, 95%CI: 1.0-6.85, P = 0.0091), and distant recurrence (mean copy number 3.94 vs 0.0025, 95%CI: 1.0-6.84, P = 0.0092). Patients who remained disease-free had higher levels of DOK-6 expression compared to those who died from breast cancer.

CONCLUSION: Decreasing expression levels of DOK-2 and DOK-6 with increased breast tumour progression supports the notion that DOK-2 and DOK-6 behave as tumour suppressors in human breast cancer.

Loss of DOK2 induces carboplatin resistance in ovarian cancer via suppression of apoptosis

OBJECTIVE

Ovarian cancers are highly heterogeneous and while chemotherapy is the preferred treatment many patients are intrinsically resistant or quickly develop resistance. Furthermore, all tumors that recur ultimately become resistant. Recent evidence suggests that epigenetic deregulation may be a key factor in the onset and maintenance of chemoresistance. We set out to identify epigenetically silenced genes that affect chemoresistance.

METHODS

The epigenomes of a total of 45 ovarian samples were analyzed to identify epigenetically altered genes that segregate with platinum response, and further filtered with expression data to identify genes that were suppressed. A tissue culture carboplatin resistance screen was utilized to functionally validate this set of candidate platinum resistance genes.

RESULTS

Our screen correctly identified 19 genes that when suppressed altered the chemoresistance of the cells in culture. Of the genes identified in the screen we further characterized one gene, docking protein 2 (DOK2), an adapter protein downstream of tyrosine kinase, to determine if we could elucidate the mechanism by which it increased resistance. The loss of DOK2 decreased the level of apoptosis in response to carboplatin. Furthermore, in cells with reduced DOK2, the level of anoikis was decreased.

CONCLUSIONS

We have developed a screening methodology that analyzes the epigenome and informatically identifies candidate genes followed by in vitro culture screening of the candidate genes. To validate our screening methodology we further characterized one candidate gene, DOK2, and showed that loss of DOK2 induces chemotherapy resistance by decreasing the level of apoptosis in response to treatment.