Caspase-2 deficiency promotes aberrant DNA-damage response and genetic instability

Abstract

Caspase-2 is an initiator caspase, which has been implicated to function in apoptotic and non-apoptotic signalling pathways, including cell-cycle regulation, DNA-damage signalling and tumour suppression. We previously demonstrated that caspase-2 deficiency enhances E1A/Ras oncogene-induced cell transformation and augments lymphomagenesis in the ElMyc mouse model. Caspase-2 À / À mouse embryonic fibroblasts (casp2 À / À MEFs) show aberrant cell-cycle checkpoint regulation and a defective apoptotic response following DNA damage. Disruption of cell-cycle checkpoints often leads to genomic instability (GIN), which is a common phenotype of cancer cells and can contribute to cellular transformation. Here we show that caspase-2 deficiency results in increased DNA damage and GIN in proliferating cells. Casp2 À / À MEFs readily escape senescence in culture and exhibit increased micronuclei formation and sustained DNA damage during cell culture and following c-irradiation. Metaphase analyses demonstrated that a lack of caspase-2 is associated with increased aneuploidy in both MEFs and in ElMyc lymphoma cells. In addition, casp2 À / À MEFs and lymphoma cells exhibit significantly decreased telomere length. We also noted that loss of caspase-2 leads to defective p53-mediated signalling and decreased trans-activation of p53 target genes upon DNA damage. Our findings suggest that loss of caspase-2 serves as a key function in maintaining genomic integrity, during cell proliferation and following DNA damage.

Caspase-2 as a tumour suppressor

“…In line with this, loss of caspase-2 slightly increases the rate of proliferation in primary, spontaneously immortalized and E1A/Ras-transformed MEFs, suggesting defective cell cycle regulation in caspase-2-deficient cells. 15,32 Consistent with their increased proliferation rate, E1A/Ras-transformed Casp2 À / À MEFs displayed an increased ability to form colonies in soft agar. 15 Interestingly, this enhanced ability of anchorage-independent growth in E1A/Ras-transformed Casp2 À / À MEFs coincides with an increased tumorigenic potential.…”

“…23 In line with aberrant growth signalling and an increased susceptibility to transform in the absence of caspase-2, primary Casp2 À / À MEFs were found to rapidly undergo spontaneous immortalization in culture. 32 These findings suggest that loss of caspase-2 is associated with deregulation of cell proliferation. This tendency to rapidly immortalize in culture most likely stems from the ability of Casp2 À / À MEFs to readily escape replicative senescence.…”

“…This tendency to rapidly immortalize in culture most likely stems from the ability of Casp2 À / À MEFs to readily escape replicative senescence. 32 Interestingly, escape from senescence coincided with reduced expression of the anti-proliferative cyclin-dependent kinase inhibitors p19 ARF , p16 INK4a and p21 CIP1/WAF1 in latepassage Casp2 À / À MEFs. 32 These findings suggest that caspase-2 may protect against cell transformation by regulation of senescence, a known mechanism that prevents the propagation of cells harbouring potentially harmful mutations or experiencing oncogenic stress.…”

“…32 Interestingly, escape from senescence coincided with reduced expression of the anti-proliferative cyclin-dependent kinase inhibitors p19 ARF , p16 INK4a and p21 CIP1/WAF1 in latepassage Casp2 À / À MEFs. 32 These findings suggest that caspase-2 may protect against cell transformation by regulation of senescence, a known mechanism that prevents the propagation of cells harbouring potentially harmful mutations or experiencing oncogenic stress. 23 In line with these findings, caspase-2-deficient tumours from mice have been shown to display an increased proliferation rate (unpublished data).…”

“…Nevertheless, some in vitro studies have provided robust experimental evidence that caspase-2 regulates the p53-dependent DDR. 32,34 Following treatment with ionizing radiation, Casp2 À / À MEFs show impaired transactivation of p53 target genes involved in cell cycle arrest and apoptosis, including puma, noxa and p21 CIP1/WAF1 . 32 Impaired p53 activity in the absence of caspase-2 may partly explain cell proliferation defects and attenuated DDR in Casp2 À / À MEFs.…”