Short- and long-term effects of radiation exposure at low dose and low dose rate in normal human VH10 fibroblasts.

Introduction: Experimental studies complement epidemiological data on the biological effects of low doses and dose rates of ionizing radiation and help in determining the dose and dose rate effectiveness factor. Methods: Human VH10 skin fibroblasts exposed to 25, 50, and 100 mGy of 137Cs gamma radiation at 1.6, 8, 12 mGy/h, and at a high dose rate of 23.4 Gy/h, were analyzed for radiation-induced short- and long-term effects. Two sample cohorts, i.e., discovery (n = 30) and validation (n = 12), were subjected to RNA sequencing. The pool of the results from those six experiments with shared conditions (1.6 mGy/h; 24 h), together with an earlier time point (0 h), constituted a third cohort (n = 12). Results: The 100 mGy-exposed cells at all abovementioned dose rates, harvested at 0/24 h and 21 days after exposure, showed no strong gene expression changes. DMXL2, involved in the regulation of the NOTCH signaling pathway, presented a consistent upregulation among both the discovery and validation cohorts, and was validated by qPCR. Gene set enrichment analysis revealed that the NOTCH pathway was upregulated in the pooled cohort (p = 0.76, normalized enrichment score (NES) = 0.86). Apart from upregulated apical junction and downregulated DNA repair, few pathways were consistently changed across exposed cohorts. Concurringly, cell viability assays, performed 1, 3, and 6 days post irradiation, and colony forming assay, seeded just after exposure, did not reveal any statistically significant early effects on cell growth or survival patterns. Tendencies of increased viability (day 6) and reduced colony size (day 21) were observed at 12 mGy/h and 23.4 Gy/min. Furthermore, no long-term changes were observed in cell growth curves generated up to 70 days after exposure. Discussion: In conclusion, low doses of gamma radiation given at low dose rates had no strong cytotoxic effects on radioresistant VH10 cells.

Development of Multidrug Resistance in Acute Myeloid Leukemia Is Associated with Alterations of the LPHN1/GAL-9/TIM-3 Signaling Pathway.

P-glycoprotein (known as ABCB1 transporter) expression in myeloid blasts of acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) leads to the commonly observed multidrug resistance. Overexpression of latrophilin-1 was detected in leukemic cells from AML patients. In a previous study, we showed that ABCB1 overexpression is associated with decreased latrophilin-1 expression in MOLM-13/VCR and SKM-1/VCR AML cell variants derived from MOLM-13 and SKM-1 cells by vincristine selection/adaptation. In the present study, we found that if ABCB1 overexpression occurs in myeloid blasts of newly diagnosed MDS patients, latrophilin-1 expression is attenuated. Latrophilin-1 may initiate TIM-3- and galectin-9-mediated immune escape. We demonstrated changes in the expression of both proteins by comparing ABCB1-positive cell variants (MOLM-13/VCR, SKM-1/VCR) with their ABCB1-negative counterparts. Galectin-9 was present in our cell lines in eight protein isoforms for which we identified the respective transcription variants resulting from alternative splicing, and we verified their structure by sequencing. The isoform profile of galectin-9 was different between ABCB1-positive and ABCB1-negative cell variants. The interaction partner of galectin-9 is CD44, and its expression was altered in the ABCB1-positive variants MOLM-13/VCR and SKM-1/VCR compared to their ABCB1-negative counterparts.

Overexpression of the ABCB1 drug transporter in acute myeloid leukemia cells is associated with downregulation of latrophilin-1.

Finding new markers with appropriate prognostic levels for the differential diagnosis of neoplastic diseases represents an important issue for biomedical research. Recently, latrophilin-1 (LPHN1) was reported to be expressed in human monocytic leukemia cell lines and in primary human acute myeloid leukemia (AML) cells. However, this expression was found to be absent in healthy leukocytes. LPHN1 was therefore considered a novel biomarker of human AML. In previous papers, we established two P-gp-positive variants (SKM-1/VCR and MOLM-13/VCR) of AML cell lines derived from parental human AML cells SKM-1 and MOLM-13 by selection with VCR. The present paper addresses the measurement of LPHN1 expression in SKM-1 and MOLM-13 cells and their P-gp-positive variants. Both parental AML lines were positive for LPHN1 expression at the mRNA and protein levels. However, the expression of LPHN1 at both the mRNA and protein levels was reduced in both P-gp-positive SKM-1/VCR and MOLM-13/VCR variants of AML cells. Interestingly, we observed an elevation of the latrophilin-3 transcript in P-gp-positive variants of AML cell lines. The combined results suggest that alterations in latrophilin expression occur in AML cells expressing P-gp.