The chromatin structuring protein HMGA2 influences human subtelomere stability and cancer chemosensitivity

Abstract

4The transient build-up of DNA supercoiling during the translocation of replication forks 3 5 threatens genome stability and is controlled by DNA topoisomerases (TOPs). This crucial 3 6 process has been exploited with TOP poisons for cancer chemotherapy. However, 3 7 pinpointing cellular determinants of the best clinical response to TOP poisons still remains 3 8 enigmatic. Here, we present an integrated approach and demonstrate that endogenous and 3 9 exogenous expression of the oncofetal high-mobility group AT-hook 2 (HMGA2) protein 4 0 exhibited broad protection against the formation of hydroxyurea-induced DNA breaks in 4 1 various cancer cells, thus corroborating our previously proposed model in which HMGA2 4 2 functions as a replication fork chaperone that forms a protective DNA scaffold at or close to 4 3 stalled replication forks. We now further demonstrate that high levels of HMGA2 also 4 4 protected cancer cells against DNA breaks triggered by the clinically important TOP1 poison 4 5 irinotecan. This protection is most likely due to the recently identified DNA supercoil 4 6 constraining function of HMGA2 in combination with exclusion of TOP1 from binding to 4 7 supercoiled substrate DNA. In contrast, low to moderate HMGA2 protein levels surprisingly 4 8 potentiated the formation of irinotecan-induced genotoxic covalent TOP1-DNA cleavage 4 9 8 1

Oncofetal HMGA2 attenuates genotoxic damage induced by topoisomerase II target compounds through the regulation of local DNA topology

“…The clinical data revealed that HMGA2 expression in leukemic cells in vivo is an independent negative predictor of disease relapse and patient survival (Marquis et al , ). Taken together with our previous HMGA2 studies investigating TOP1 poisons and DNA synthesis inhibitors (Ahmed et al , ; Yu et al , ), our current study strongly enforces the clinical importance of HMGA2 as a prognostic therapeutic marker in the clinic and as an important drug target.…”

“…Our previous studies have shown that HMGA2 functions as a replication fork chaperone when replication is challenged by the DNA synthesis inhibitor HU (Yu et al , ). However, HMGA2 differentially affects the genotoxic efficacy of the clinically relevant TOP1 poison irinotecan/SN38, and we mechanistically ascribed these different phenotypic outcomes of drug treatment to ternary complex formation between HMGA2, TOP1, and scDNA substrates (Ahmed et al , ). Here, by employing our four previously established cancer cell models, we first investigated whether HMGA2 affects DNA damage caused by the clinically relevant TOP2 poison Etop.…”

“…We found that the expression of HMGA2 always reduced the occurrence of DSBs that generated the drug‐induced 30–100 kb DNA fragments across all four cancer cell model systems. These models exhibit differential HMGA2 expression levels due to either HMGA2 knockout (H1299 cells), HMGA2 knockdown (HT1080 cells), or HMGA2 overexpression (HeLa and A549 cells) (Ahmed et al , ). Furthermore, human HMGA2 expressed from a transiently transfected vector in parental HeLa cells that do not express detectable levels of endogenous HMGA2 confirmed a specific protective function of HMGA2 against Etop‐induced DNA breaks (Fig.…”

“…Human HMGA2‐expressing clones A549 (1.3/1.5/1.6) and HeLa (P2/P8/P19) have been described previously (Summer et al , ). H1299 HMGA2 KO cells were generated by CRISPR‐Cas9 and have also been described previously (Ahmed et al , ).…”

“…Besides important regulatory roles in gene expression, in particular during embryonic/fetal development and tumorigenesis/metastasis in the adult organism (Droge and Davey, ; Fusco and Fedele, ; Pfannkuche et al , ; Sgarra et al , ), HMGA2 has also been implicated in DNA base excision repair (Summer et al , ) and DNA damage repair signaling pathways (Hombach‐Klonisch et al , ; Natarajan et al , ; Palmieri et al , ), hinting at important functions for HMGA2 in genome stability following genotoxic stress conditions. In this context, fast proliferation rates of cancer cells enhance DNA replication stress (Gaillard et al , ), and we have recently demonstrated that HMGA2 broadly protects hydroxyurea (HU)‐induced stalled replication forks from collapse into genotoxic DSBs in human cancer and stem cells, thus implying that HMGA2 is also involved upstream of DNA repair processes as a first line of defense to prevent genome instability (Ahmed et al , ; Yu et al , ).…”