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BCCIP suppresses tumor initiation but is required for tumor progression.

ABSTRACT: Dysfunctions of genome caretaker genes contribute to genomic instability and tumor initiation. Because many of the caretaker genes are also essential for cell viability, permanent loss of function of these genes would prohibit further tumor progression. How essential caretaker genes contribute to tumorigenesis is not fully understood. Here, we report a "hit-and-run" mode of action for an essential caretaker gene in tumorigenesis. Using a BRCA2-interacting protein BCCIP as the platform, we found that a conditional BCCIP knockdown and concomitant p53 deletion caused rapid development of medulloblastomas, which bear a wide spectrum of alterations involving the Sonic Hedgehog (Shh) pathway, consistent with a caretaker responsibility of BCCIP on genomic integrity. Surprisingly, the progressed tumors have spontaneously lost the transgenic BCCIP knockdown cassette and restored BCCIP expression. Thus, a transient downregulation of BCCIP, but not necessarily a permanent mutation, is sufficient to initiate tumorigenesis. After the malignant transformation has been accomplished and autonomous cancer growth has been established, BCCIP reverses its role from a tumor-initiation suppressor to become a requisite for progression. This exemplifies a new type of tumor suppressor, which is distinct from the classical tumor suppressors that are often permanently abrogated during tumorigenesis. It has major implications on how a nonmutagenic or transient regulation of essential caretaker gene contributes to tumorigenesis. We further suggest that BCCIP represents a paradoxical class of modulators for tumorigenesis as a suppressor for initiation but a requisite for progression (SIRP).

SUBMITTER: Huang YY

PROVIDER: S-EPMC3918420 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature

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BCCIP suppresses tumor initiation but is required for tumor progression.

Huang Yi-Yuan YY Dai Li L Gaines Dakim D Droz-Rosario Roberto R Lu Huimei H Liu Jingmei J Shen Zhiyuan Z

Cancer research 20131021 23

Dysfunctions of genome caretaker genes contribute to genomic instability and tumor initiation. Because many of the caretaker genes are also essential for cell viability, permanent loss of function of these genes would prohibit further tumor progression. How essential caretaker genes contribute to tumorigenesis is not fully understood. Here, we report a "hit-and-run" mode of action for an essential caretaker gene in tumorigenesis. Using a BRCA2-interacting protein BCCIP as the platform, we found ...[more]

PMID: 24145349

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Project description:Prostate cancer (PrCa) is one of the most common malignancies in Western countries. However, the pathways that promote invasion, especially in late-stage castration-resistant PrCa (CRPC), are poorly understood. Heat shock factors (HSFs) are transcriptional regulators essential for cell survival upon proteotoxic stress, and HSF1 is also identified as a driver of oncogenesis. Here, our aim was to elucidate the molecular mechanisms that contribute to CRPC and invasion. In silico analyses showed that high HSF1 expression levels correlate with poor survival and high Gleason score in PrCa. In the same data set, HSF2, which has not previously been linked to cancer, displayed decreased expression. Using 3-dimensional (3D) organotypic PrCa cultures that spontaneously undergo an invasive conversion, opposite effects of HSF1 and HSF2 were observed; tumor spheroids lacking HSF1 grew slowly, were polarized and devoid of invasive structures, and depletion of HSF2 potentiated invasiveness. In the in vivo xenograft chorioallantoic membrane model, HSF1 silencing caused tumor regression and fibrosis, and knockdown of HSF2 generated large invasive tumors, verifying the results from the 3D-cultures. Gene expression profiling revealed enrichment of genes connected to translational control when either HSF1 or HSF2 was silenced. HSF1-specific targets were associated with progression of tumorigenesis, whereas HSF2 targets were involved in focal adhesion, critical for invasion. This study provides the first evidence for HSF2 functioning in cancer, i.e. as a tumor suppressor. Moreover, human PrCa tissue microarrays demonstrated increased nuclear HSF1 expression, which significantly correlated with high-grade Gleason score. Cytoplasmic HSF1 was detected in a subset of tumors and intriguingly, correlated with decreased disease-specific survival. This was most pronounced in intermediate Gleason score 7 tumors and in metastases. We propose the use of HSF1 as a biomarker to predict PrCa outcome, thus facilitating clinical decision-making and supporting individualized treatment choices. HSF1 and HSF2 siRNA transfection was performed in triplicates (biological replicates), for 5 and 8 days prior to harvesting total RNA; and compared to PC-3 cells transfected with scrambled control siRNAs for 5 and 8 days, respectively.

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BCCIP suppresses tumor initiation but is required for tumor progression.

Publications

BCCIP suppresses tumor initiation but is required for tumor progression.

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