Apoptotic caspases inhibit abscopal responses to radiation and identify a new prognostic biomarker for breast cancer patients

Abstract

Caspase 3 (CASP3) has a key role in the execution of apoptosis, and many cancer cells are believed to disable CASP3 as a mechanism of resistance to cytotoxic therapeutics. Alongside, CASP3 regulates stressresponsive immunomodulatory pathways, including secretion of type I interferon (IFN). Here, we report that mouse mammary carcinoma TSA cells lacking Casp3 or subjected to chemical caspase inhibition were as sensitive to the cytostatic and cytotoxic effects of radiation therapy (RT) in vitro as their control counterparts, yet secreted increased levels of type I IFN. This effect originated from the accrued accumulation of irradiated cells with cytosolic DNA, likely reflecting the delayed breakdown of cells experiencing mitochondrial permeabilization in the absence of CASP3. Casp3-/-TSA cells growing in immunocompetent syngeneic mice were more sensitive to RT than their CASP3-proficient counterparts, and superior at generating bona fide abscopal responses in the presence of an immune checkpoint blocker. Finally, multiple genetic signatures of apoptotic proficiency were unexpectedly found to have robust negative (rather than positive) prognostic significance in a public cohort of breast cancer patients. However, these latter findings were not consistent with genetic signatures of defective type I IFN signaling, which were rather associated with improved prognosis. Differential gene expression analysis on patient subgroups with divergent prognosis (as stratified by independent signatures of apoptotic proficiency) identified SLC7A2 as a new biomarker with independent prognostic value in breast cancer patients. With the caveats associated with the retrospective investigation of heterogeneous, public databases, our data suggest that apoptotic caspases may influence the survival of breast cancer patients (or at least some subsets thereof) via mechanisms not necessarily related to type I IFN signaling as they identify a novel independent prognostic biomarker that awaits prospective validation.

Immunogenicity of cell death driven by immune effectors

“…that are deficient in cross-priming as a consequence of stimulator of interferon response cGAMP interactor 1 (Sting1) or basic leucine zipper transcription factor, ATF-like 3 (Batf3) deletion. 5 6 Conversely, the results from Pardo and colleagues appear to challenge the current literature in proposing that caspase 3 (CASP3), a key regulator of apoptosis with multipronged immunosuppressive effects including the ability to shut down type I interferon production by STING1, [8][9][10] is required for the immunogenicity of cancer cells succumbing to immune effectors. 5 This interpretation was based on the ability of chemical pan-caspase inhibitor (Q-VD-OPh) and a dominant-negative variant of CASP3, but not the overexpression of BCL2-like 1 (BCL2L1, a potent antiapoptotic molecule best known as BCL-X L ), to reduce (to some degree) immunological protection conferred by cancer cells dying on attack by antigen-specific CTLs.…”

“…5 Thus, the impact of CASP3 on the efficacy of vaccination with cancer cells succumbing to CTLs and NK cells appears to be largely limited to its ability to precipitate cell death in this setting, which does not apply to ICD driven by other stimuli including radiation. [8][9][10] Early work from the late Jurg Tschopp and colleagues demonstrated that the lytic granules of CTLs contain high levels of CALR, which was interpreted as a safeguard mechanism to prevent PRF1 activation by Ca 2+ ions prior to granule exocytosis, largely relying on the ability of CALR to chelate Ca 2+ . 11 Thus, it is possible that (at least part of) the CALR molecules detected on the surface of cancer cells attacked by CTLs (or NK cells) may be provided in trans by the latter (rather than in cis by the former) along with PRF1 and the other cytotoxic molecules contained in lytic granules.…”

Apoptotic caspases cut down the immunogenicity of radiation

“…However, the clonogenic potential of Casp3 −/-TSA cells and TSA cells exposed to the pan-caspase inhibitor Z-Val-Ala-Asp fluoromethyl ketone (Z-VAD-fmk) was compromised by low-dose irradiation comparably to that of their control counterparts. 9 These data confirm that apoptotic caspases control the kinetic of apoptotic cell death driven by radiation therapy, but have little impact on the ultimate fate of irradiated cells.…”

IRLnc: A novel functional noncoding RNA contributes to intramuscular fat deposition

“…One gene named LRRC66 was are involved in diverse biological processes, including cell adhesion, cellular tra cking, and hormone-receptor interactions [22]. And other genes were mainly associated with diseases such as Mucopolysaccharidosis IIIB [23], stress-induced injury [24], oral-facial-digital syndromes [25], and breast cancer [26]. From the results, intramuscular related genes involved in fat and muscle related function were consistent with previous research, which reported that IMF is regulated through a complex pathway that interacts with muscle, fat, and connective tissue [27,28].…”