Missense mutations in TP53 gene promote metastasis in human tumours. However, little is known about the complete loss of function of p53 in tumour metastasis. Here we show that squamous cell carcinomas generated by the specific ablation of Trp53 gene in mouse epidermis are highly metastatic. Biochemical and genome-wide mRNA and miRNA analyses demonstrated that metastases are associated with the early induction of epithelial-mesenchymal transition (EMT) and deregulated miRNA expression in primary tumours. Increased expression of miR-21 was observed in undifferentiated, prometastatic mouse tumours and in human tumours characterized by p53 mutations and distant metastasis. The augmented expression of miR-21, mediated by active mTOR and Stat3 signalling, conferred increased invasive properties to mouse keratinocytes in vitro and in vivo, whereas blockade of miR-21 in a metastatic spindle cell line inhibits metastasis development. Collectively these data identify novel molecular mechanisms leading to metastasis in vivo originated by p53 loss in epithelia.
Head and neck squamous cell carcinoma (HNSCC) is a common human neoplasia with poor prognosis and survival that frequently displays Akt overactivation. Here we show that mice displaying constitutive Akt activity (myrAkt) in combination with Trp53 loss in stratified epithelia develop oral cavity tumors that phenocopy human HNSCC. The myrAkt mice develop oral lesions, making it a possible model of human oral dysplasia. The malignant conversion of these lesions, which is hampered due to the induction of premature senescence, is achieved by the subsequent ablation of Trp53 gene in the same cells in vivo. Importantly, mouse oral tumors can be followed by in vivo imaging, show metastatic spreading to regional lymph nodes, and display activation of nuclear factor-KB and signal transducer and activator of transcription-3 pathways and decreased transforming growth factor-B type II receptor expression, thus resembling human counterparts. In addition, malignant conversion is associated with increased number of putative tumor stem cells. These data identify activation of Akt and p53 loss as a major mechanism of oral tumorigenesis in vivo and suggest that blocking these signaling pathways could have therapeutic implications for the management of HNSCC.
Our experiments have focused on the analysis of residual haematopoietic damage in 8-day-old and 12-week-old mice X-irradiated with a single dose of 7 Gy. In the case of the adult mice, analysis of the femoral and splenic CFU-S, CFU-GM and BFU-E showed a persistent depletion of these haematopoietic progenitor cells after irradiation. In contrast, in 1-week-old irradiated mice, a progressive recovery of the femoral haematopoietic progenitors was observed, achieving essentially normal values 1 year after irradiation. The spleens of these mice, however, contained significantly less haematopoietic progenitors than the control group, mainly as a consequence of the size reduction of this organ. In the peripheral blood, normal cellularity values were observed in most cases, although in the adult group a decline in numbers or circulating cells was noted after the first year following irradiation. Long-term bone marrow cultures (LTBMCs) established 1 year after the irradiation of adult mice generated poor adherent layers, while confluent stromas were observed in flasks corresponding to 8-day-old irradiated mice. Analyses of the functional activity of granulocytes obtained from either the peripheral blood or LTBMCs revealed that both young and adult irradiated mice produced granulocytes generating high levels of superoxide anion, in relation to age-matched controls. This finding was correlated with a long-term microenvironmental activation which resulted in an overproduction of granulocyte-macrophage colony-stimulating factor.
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