The autotaxin–LPA 2 GPCR axis is modulated by γ-irradiation and facilitates DNA damage repair

Abstract

In this study we characterized the effects of radiation injury on the expression and function of the autotaxin (ATX)-LPA2 GPCR axis. In IEC-6 crypt cells and jejunum enteroids quantitative RT-PCR showed a time- and dose-dependent upregulation of lpa2 in response to γ-irradiation that was abolished by mutation of the NF-κB site in the lpa2 promoter or by inhibition of ATM/ATR kinases with CGK-733, suggesting that lpa2 is a DNA damage response gene upregulated by ATM via NF-κB. The resolution kinetics of the DNA damage marker γ-H2AX in LPA-treated IEC-6 cells exposed to γ-irradiation was accelerated compared to vehicle, whereas pharmacological inhibition of LPA2 delayed the resolution of γ-H2AX. In LPA2-reconstituted MEF cells lacking LPA1&3 the levels of γ-H2AX decreased rapidly, whereas in Vector MEF were high and remained sustained. Inhibition of ERK1&2 or PI3K/AKT signaling axis by pertussis toxin or the C311A/C314A/L351A mutation in the C-terminus of LPA2 abrogated the effect of LPA on DNA repair. LPA2 transcripts in Lin−Sca-1+c-Kit+ enriched for bone marrow stem cells were 27- and 5-fold higher than in common myeloid or lymphoid progenitors, respectively. Furthermore, after irradiation higher residual γ-H2AX levels were detected in the bone marrow or jejunum of irradiated LPA2-KO mice compared to WT mice. We found that γ-irradiation increases plasma ATX activity and LPA level that is in part due to the previously established radiation-induced upregulation of TNFα. These findings identify ATX and LPA2 as radiation-regulated genes that appear to play a physiological role in DNA repair.

Implications for breast cancer treatment from increased autotaxin production in adipose tissue after radiotherapy

“…Previous work has indicated that ATX activity was not increased in white adipose tissue of mice at 4 h after exposure to 6 Gy (34); however, we showed that the maximum increases of ATX mRNA occurred with 1 Gy of radiation after 24 h and that this resulted in the increased secretion of ATX protein and activity at 48 h. Our results establish that even low‐dose irradiation (0.25–1 Gy) of adipose tissue set up a potentially feedforward inflammatory cycle via the production of LPA and other inflammatory mediators, which could further increase ATX secretion (Fig. 10).…”

“…LPA also protects cells from radiation‐induced cell death (1, 34–36). This protection involves increased signaling via LPA 2 receptors, which protect against apoptosis by stimulating prosurvival kinase pathways that involve thyroid receptor‐interacting protein‐6 and depleting cells of Siva‐1, a proapoptotic signaling protein (35).…”

“…This protection involves increased signaling via LPA 2 receptors, which protect against apoptosis by stimulating prosurvival kinase pathways that involve thyroid receptor‐interacting protein‐6 and depleting cells of Siva‐1, a proapoptotic signaling protein (35). LPA also facilitates DNA repair (34). This facilitation involves an increase in Nrf2 expression (50), which promotes the synthesis of genes that promote DNA repair (51, 52).…”

“…Previous work using IEC‐6 crypt cells and jejunum enteroids has indicated that radiation increased the expression of LPA 2 receptors, which are important in protecting against radiation‐induced cell death. It was concluded that this effect depended on the activation of ATM on the basis of using CGK733 (34); however, this inhibitor also inhibits ATR. We used CGK733 and also the specific inhibitors for ATM and ATR, and KU55933 and VE‐821, respectively.…”

Lysophosphatidic acid type 2 receptor agonists in targeted drug development offer broad therapeutic potential

“…Vehicle-treated LPA 2 KO mice showed more extensive damage in their crypt counts and a higher number of apoptotic cells compared with WT or LPA 1 KO mice. We also found that LPA 2 KO mice showed delayed resolution of DNA double-strand breaks (28). This suggests that LPA 2 is important in the natural protection against radiation, mediated in part by augmenting the DNA damage repair (DDR) response.…”