Gal-1 promotes lung cancer cell survival by enhancing PARP1/H1.2 interaction to promote DNA repair upon DNA damage response

Galectin-1 (Gal-1), a member of the galectin family, has emerged as a regulator of tumor progression. Several studies have reported the up-regulation of Gal-1 expression in multiple cancer cells and its promotion on tumor proliferation. However, the mechanism by which Gal-1 promotes tumor growth remains to be thoroughly understood. In this study, it was discovered that high expression of Gal-1 in viral cancers was inversely correlated with the overall survival of patients. Through constructing Gal-1-overexpressing cell lines, it was uncovered that cell proliferation and colony formation were significantly improved. The results of transcriptomic and proximity-labeling-based proteomic analyses indicated that Gal-1 interacted with PARP1 and histone H1.2 in lung cancer cells. In the case of etoposide treatment leading to DNA double-strand breaks, Gal-1 accelerated the degradation of H1.2 by enhancing its interaction with PARP1 and promoting its PARylation modification. It caused the activation of downstream DNA repair pathways such as the ATM and NBS1 signaling pathways, thus reducing apoptosis. Moreover, Gal-1 inhibitors TDG and OTX008 could restore cell sensitivity to etoposide. This study provides new clues for the role of Gal-1 in the development of tumors and renders suggestions for the treatment of patients with high Gal-1 expression in the clinic.

Methods
Proximity-labeling MS and analysis

The stable Galectin-1-TurboID-NLS-Flag A549 cells were incubated with 500μM biotin， 5 mM MgCl2, and 1 mM ATP for 12h. The cells were harvested and washed, then lysed with the IP lysis buffer. The lysate was incubated with blocked streptavidin beads(Smart-Lifesciences,#SM017K01) with a rotator at 4℃ overnight. Then, wash the beads following the kit`s protocols. 10% of the beads, which were eluted by 1×SDS loading buffer and boiled for 10 mins, were used for to silver stain assay and Immunoblotting. The rest 90% of the beads were sent to the Wuhan University instrument and equipment sharing platform for MS analysis.

RNA seq and analysis

Total RNA was extracted from cells with the indicated treatment and sent to BGI to construct a single-stranded circular DNA library. The constructed library is qualitatively inspected, and sequencing is carried out after it is qualified.