DNp73 exerts function in metastasis initiation by disconnecting the inhibitory role of EPLIN on IGF1R-AKT/STAT3 signaling.

Dissemination of cancer cells from primary tumors is the key event in metastasis, but specific determinants are widely unknown. Here, we show that DNp73, an inhibitor of the p53 tumor suppressor family, drives migration and invasion of nonmetastatic melanoma cells. Knockdown of endogenous DNp73 reduces this behavior in highly metastatic cell lines. Tumor xenografts expressing DNp73 show a higher ability to invade and metastasize, while growth remains unaffected. DNp73 facilitates an EMT-like phenotype with loss of E-cadherin and Slug upregulation. We provide mechanistic insight toward regulation of LIMA1/EPLIN by p73/DNp73 and demonstrate a direct link between the DNp73-EPLIN axis and IGF1R-AKT/STAT3 activation. These findings establish initiation of the invasion-metastasis cascade via EPLIN-dependent IGF1R regulation as major activity of DNp73.

E2F1 in melanoma progression and metastasis.

Metastases are responsible for cancer deaths, but the molecular alterations leading to tumor progression are unclear. Overexpression of the E2F1 transcription factor is common in high-grade tumors that are associated with poor patient survival. To investigate the association of enhanced E2F1 activity with aggressive phenotype, we performed a gene-specific silencing approach in a metastatic melanoma model. Knockdown of endogenous E2F1 via E2F1 small hairpin RNA (shRNA) expression increased E-cadherin expression of metastatic SK-Mel-147 melanoma cells and reduced their invasive potential but not their proliferative activity. Although growth rates of SK-Mel-147 and SK-Mel-103 xenograft tumors expressing E2F1 shRNA or control shRNA were similar, mice implanted with cells expressing E2F1 shRNA had a smaller area of metastases per lung than control mice (n = 3 mice per group; 5% vs 46%, difference = 41%, 95% confidence interval = 15% to 67%; P = .01; one-way analysis of variance). We identified epidermal growth factor receptor as a direct target of E2F1 and demonstrated that inhibition of receptor signaling abrogates E2F1-induced invasiveness, emphasizing the importance of the E2F1-epidermal growth factor receptor interaction as a driving force in melanoma progression that may serve as a paradigm for E2F1-induced metastasis in other human cancers.

Mutational analysis of Chk1, Chk2, Apaf1 and Rb1 in human malignant melanoma cell lines.

Four tumour suppressor genes (Chk1, Chk2, Apaf1 and Rb1) in nine human malignant melanoma cell lines were screened for a loss of gene expression, point mutations and small deletions/insertions by cDNA-based DGGE/SCCP analysis. In two cell lines alterations of the investigated genes could be demonstrated. This result confirms our assumption of the participation of dysfunctional p53 inducer/effector genes in human melanoma aetiology. Furthermore, it points towards the probable principal role of diverse alternative p53-pathway disruption mechanisms in this highly therapy-resistant malignancy without affecting p53 itself. To our knowledge, this is the first CHK1/CHK2 mutation screening in human melanoma.