Elephant TP53-RETROGENE 9 induces transcription-independent apoptosis at the mitochondria.

Approximately 20 TP53 retrogenes exist in the African and Asian elephant genomes (Loxodonta Africana, Elephas Maximus) in addition to a conserved TP53 gene that encodes a full-length protein. Elephant TP53-RETROGENE 9 (TP53-R9) encodes a p53 protein (p53-R9) that is truncated in the middle of the canonical DNA binding domain. This C-terminally truncated p53 retrogene protein lacks the nuclear localization signals and oligomerization domain of its full-length counterpart. When expressed in human osteosarcoma cells (U2OS), p53-R9 binds to Tid1, the chaperone protein responsible for mitochondrial translocation of human p53 in response to cellular stress. Tid1 expression is required for p53-R9-induced apoptosis. At the mitochondria, p53-R9 binds to the pro-apoptotic BCL-2 family member Bax, which leads to caspase activation, cytochrome c release, and cell death. Our data show, for the first time, that expression of this truncated elephant p53 retrogene protein induces apoptosis in human cancer cells. Understanding the molecular mechanism by which the additional elephant TP53 retrogenes function may provide evolutionary insight that can be utilized for the development of therapeutics to treat human cancers.

High OCT4A levels drive tumorigenicity and metastatic potential of medulloblastoma cells.

Medulloblastoma is a highly aggressive pediatric brain tumor, in which sporadic expression of the pluripotency factor OCT4 has been recently correlated with poor patient survival. However the contribution of specific OCT4 isoforms to tumor aggressiveness is still poorly understood. Here, we report that medulloblastoma cells stably overexpressing the OCT4A isoform displayed enhanced clonogenic, tumorsphere generation, and invasion capabilities. Moreover, in an orthotopic metastatic model of medulloblastoma, OCT4A overexpressing cells generated more developed, aggressive and infiltrative tumors, with tumor-bearing mice attaining advanced metastatic disease and shorter survival rates. Pro-oncogenic OCT4A effects were expression-level dependent and accompanied by distinct chromosomal aberrations. OCT4A overexpression in medulloblastoma cells also induced a marked differential expression of non-coding RNAs, including poorly characterized long non-coding RNAs and small nucleolar RNAs. Altogether, our findings support the relevance of pluripotency-related factors in the aggravation of medulloblastoma traits classically associated with poor clinical outcome, and underscore the prognostic and therapeutic value of OCT4A in this challenging type of pediatric brain cancer.

High OCT4A levels drive tumorigenicity and metastatic potential of medulloblastoma cells

Medulloblastoma is a highly aggressive pediatric brain tumor, in which sporadic expression of the pluripotency factor OCT4 has been recently correlated with poor patient survival. However the contribution of specific OCT4 isoforms to tumor aggressiveness is still poorly understood. Here, we report that medulloblastoma cells stably overexpressing the OCT4A isoform displayed enhanced clonogenic, tumorsphere generation, and invasion capabilities. Moreover, in an orthotopic metastatic model of medulloblastoma, OCT4A overexpressing cells generated more developed, aggressive and infiltrative tumors, with tumor-bearing mice attaining advanced metastatic disease and shorter survival rates. Pro-oncogenic OCT4A effects were expression-level dependent and accompanied by distinct chromosomal aberrations. OCT4A overexpression in medulloblastoma cells also induced a marked differential expression of non-coding RNAs, including poorly characterized long non-coding RNAs and small nucleolar RNAs. Altogether, our findings support the relevance of pluripotency-related factors in the aggravation of medulloblastoma traits classically associated with poor clinical outcome, and underscore the prognostic and therapeutic value of OCT4A in this challenging type of pediatric brain cancer.

Embryonic Stem Cell-Related Protein L1TD1 Is Required for Cell Viability, Neurosphere Formation, and Chemoresistance in Medulloblastoma.

Misexpression of stem cell-related genes may occur in some cancer cells, influencing patient's prognosis. This is the case of medulloblastoma, a common and clinically challenging malignant tumor of the central nervous system, where expression of the pluripotency factor, OCT4, is correlated with poor survival. A downstream target of OCT4, L1TD1 (LINE-1 type transposase domain-containing protein 1 family member), encodes a novel embryonic stem cell (ESC)-related protein involved in pluripotency and self-renewal of ESCs. L1TD1 is still poorly characterized and its expression pattern and function in cancer cells are virtually unknown. Although normally restricted to non-neoplastic undifferentiated cells and germ cells, we found that high L1TD1 expression also occurs in medulloblastoma cells, reaching levels similar to those found in ESCs, and is correlated with poor prognosis. Conversely to what is reported during normal cell differentiation, when differentiated cells remain healthy, despite L1TD1 downregulation, depletion of L1TD1 protein levels by targeted gene silencing significantly reduced medulloblastoma cell viability, inhibiting cell proliferation and inducing apoptosis. More strikingly, L1TD1 depletion downregulated expression of the neural stem cell markers, CD133 and Nestin, inhibited neurosphere generation capability, and sensitized medulloblastoma cells to temozolomide and cisplatin, two chemotherapeutic agents of clinical relevance in medulloblastoma treatment. Our findings provide insights about the contribution of pluripotency-related genes to a more aggressive tumor phenotype through their involvement in the acquisition of stem-like properties by cancer cells and point out L1TD1 as a potential therapeutic target in malignant brain tumors.