Comparison of UVC Sensitivity and Dectin-2 Expression Between Malignant and Non-malignant Cells

Abstract

Background/aim: Rapid spread of COVID-19 resulted in the revision of the value of ultraviolet C (UVC) sterilization in working spaces. This study aimed at investigating the UVC sensitivity of eighteen malignant and nonmalignant cell lines, the protective activity of sodium ascorbate against UVC, and whether Dectin-2 is involved in UVC sensitivity.

Materials and methods: Various cell lines were exposed to UVC for 3 min, and cell viability was determined using the MTT assay. Anti-UV activity was determined as the ratio of 50% cytotoxic concentration (determined with unirradiated cells) to 50% effective concentration (that restored half of the UV-induced loss of viability). Dectin-2 expression was quantified using flow cytometry.

Results: The use of culture medium rather than phosphate-buffered saline is recommended as irradiation solution, since several cells are easily detached during irradiation in phosphate-buffered saline. Oral squamous cell carcinoma cell lines showed the highest UV sensitivity, followed by neuroblastoma, glioblastoma, leukemia, melanoma, lung carcinoma cells, and normal oral and dermal fibroblasts. Human dermal fibroblasts were more resistant than melanoma cell lines; however, both expressed Dectin-2. Sodium ascorbate at micromolar concentrations eliminated the cytotoxicity of UVC in these cell lines.

Conclusion: Normal cells are generally UVC-resistant compared to corresponding malignant cells, which have higher growth potential. Dectin-2 protein expression itself may not be determinant of UVC sensitivity.

Keywords: Dectin-2; UVC sensitivity; dermal fibroblast; malignancy; melanoma; protection; sodium ascorbate.

Figure 1. UVC-shielding effect of the walls of a 96-microwell plate. The 96-microplate (A) and well (B) are shown. Diagonal UVC irradiation produced the non-irradiated area (indicated by red color) (C). HSC-2 cells (3×10³/0.1 ml) were inoculated into the inner 60 wells of 12 microwell plates, and incubated for 48 h. The 11 plates were positioned at an angle of 0, 0.6, 1.2, 2.3, 3.5, 4.7, 7.0, 9.4, 14.2, 19.1 or 40.8˚ (D, E) and exposed to UVC irradiation for 8 min from a height of 555 mm. One control plate was not unirradiated. Cell viability (absorbance at 560 nm) was then determined using the MTT method (F). To visualize the cell viability more clearly especially at low angles, data were also plotted logarithmically (G). Each value represents the mean of 10 determinations.

Figure 2. Irradiation condition set up for the present study. The 96-microwell plate was placed horizontally (A) and then moved to the end of the safety cabinet (B) to allow the cells to receive the maximal intensity of UVC light.

Figure 3. Effect of type of irradiation solution and depth of solution on the sensitivity of UVC irradiation. Near-confluent HSC-2 cells received 50, 100, 150, 200 μl of PBS(–) (A~C), DMEM (D~F) or FBS (G~I), and then irradiated for 1 min (A, D, G), 2 min (B, E, H) or 3 min (C, F, I). After incubation for 48 h with 100 μl of fresh culture medium (DMEM+10%FBS), viable cell number was determined using the MTT method. Each value represents mean±S.D. (n=6).

Figure 4. Comparison of UVC sensitivity of 18 cultured cells. (A) Cells were UVC irradiated for 0 (control), 1, 2, 4, or 8 min, and then replaced with fresh culture medium to determine cell viability (absorbance at 560 mm). Each value represents mean±S.D. (n=12). (B) Data of (A) are expressed as viable cell numbers (% of control).

Figure 5. Reproducibility of the results presented in Figure 4. (A) A total of 17 cell lines (T98G, LY-PPB6, ML-1 and HL-60 cell lines presented in Figure 4 were replaced by TIG-3, HFL-1, and COLO679 cell lines) were UV irradiated for 0 (control), 2, or 4 min, and then replaced with fresh culture medium to determine cell viability (absorbance at 560 mm). Each value represents mean±S.D. (n=12). (B) Data of (A) are expressed as viable cell numbers (% of control).

Figure 6. Effect of exposure time to UVC. HDFa (20PDL) and COLO679 cells were exposed to UV for 0 (control), 1, 2, 3, 5, 7, or 10 min, and then cultured for 48 h in fresh culture medium. Data are plotted as viable cell numbers (% of control). Each value represents mean±S.D. (n=3). *p<0.05, ANOVA with Bonferroni post hoc. N.S.: not significant.

Figure 7. Surface expression of Dectin-2 in HDFa (A), CoLo679 (B), and SH-SY5Y cells (C) was quantified using flow cytometry. Red, stained with Dectin-2 antibody; Yellow, stained with control antibody; Blue, unstained.

Figure 8. Anti-UVC activity of sodium ascorbate. HDFa (26PDL) (A) and COLO679 (B) cells were exposed for 3 min with the indicated concentrations of sodium ascorbate and cultured for 48 h in fresh culture medium to determine the viable cell number. Each value represents mean±S.D. (n=3). *p<0.05, ANOVA with Bonferoni post hoc.