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EML4-ALK induces cellular senescence in mortal normal human cells and promotes anchorage-independent growth in hTERT-transduced normal human cells.

ABSTRACT:

Background

Chromosomal inversions involving anaplastic lymphoma kinase (ALK) and echinoderm microtubule associated protein like 4 (EML4) generate a fusion protein EML4-ALK in non-small cell lung cancer (NSCLC). The understanding of EML4-ALK function can be improved by a functional study using normal human cells.

Methods

Here we for the first time conduct such study to examine the effects of EML4-ALK on cell proliferation, cellular senescence, DNA damage, gene expression profiles and transformed phenotypes.

Results

The lentiviral expression of EML4-ALK in mortal, normal human fibroblasts caused, through its constitutive ALK kinase activity, an early induction of cellular senescence with accumulated DNA damage, upregulation of p16^INK4A and p21^WAF1, and senescence-associated β-galactosidase (SA-β-gal) activity. In contrast, when EML4-ALK was expressed in normal human fibroblasts transduced with telomerase reverse transcriptase (hTERT), which is activated in the vast majority of NSCLC, the cells showed accelerated proliferation and acquired anchorage-independent growth ability in soft-agar medium, without accumulated DNA damage, chromosome aberration, nor p53 mutation. EML4-ALK induced the phosphorylation of STAT3 in both mortal and hTERT-transduced cells, but RNA sequencing analysis suggested that the different signaling pathways contributed to the different phenotypic outcomes in these cells. While EML4-ALK also induced anchorage-independent growth in hTERT-immortalized human bronchial epithelial cells in vitro, the expression of EML4-ALK alone did not cause detectable in vivo tumorigenicity in immunodeficient mice.

Conclusions

Our data indicate that the expression of hTERT is critical for EML4-ALK to manifest its in vitro transforming activity in human cells. This study provides the isogenic pairs of human cells with and without EML4-ALK expression.

SUBMITTER: Miyanaga A

PROVIDER: S-EPMC7992817 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Introduction: Pleural mesothelioma (PM) is known as one of the most aggressive malignancies among all cancers, despite of usually absent tumor-driver mutations in oncogenes. It develops in a unique inflammatory tumor microenvironment (TME), which has been postulated as major contributor of PM’s highly aggressive nature. Mesothelioma-associated fibroblasts (Meso-CAFs), a main component of the TME have recently been shown to substantially stimulate several aspects of PM aggressiveness and promote the malignant transformation of pleural mesothelial cells. However, respective cell models for TME research in PM are still very limited. The most commonly used pleural mesothelial cell line Met5A has been established decades ago and patient-derived Meso-CAFs have just recently been characterized for the first time. The aim of the current study was to generate and characterize pleural mesothelial and Meso-CAF cell models with an extended life span that closely resemble the primary cells isolated from human tissue. Methods: Pleural mesothelial cells and Meso-CAFs were isolated from human tissue of pneumothorax and PM patients, respectively. Retroviral transduction was used to induce stable expression of human telomerase reverse transcriptase (hTERT) and enhanced green fluorescent protein (EGFP) in the primary cells. The established cell models were evaluated by measuring their doubling times, gene expression and protein activity levels of hTERT, as well as the absolute lengths of telomeres. The transduced cells were compared to their primary counterparts on the protein level using proteome analysis and the impact of their conditioned media (CM) on tumor cell growth was investigated by videomicroscopy. Results: All transduced derivatives exhibit elevated hTERT gene expression and protein activity, increased hTERT protein amounts in the nucleus, and moderately higher absolute telomere lengths compared to their parental primary cells. The transduction with hTERT did not elicit marked changes in the morphology of the cells, as well as in their proteomes and secretomes. The CM of primary and hTERT-transduced Meso-CAFs comparably stimulated PM cell growth, while medium conditioned by normal pleural mesothelial cells including their hTERT-transduced derivatives was not able to induce a growth stimulating effect. Conclusion: The hTERT-transduced cells closely resemble their primary counterparts, while retaining telomerase activity, thus preventing replicative senescence. The new cell models provide valuable tools for the investigation of cellular interactions cellular interactions within the TME of PM and thus may help to identify novel biomarkers for early diagnosis and to develop new therapeutic strategies.