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ST 1.3 –
Efectos biológicos de las radiaciones ionizantes y Dosimetría biológica
RADIOSENSITIZING EFFECT OF RHOB PROTEIN IN MELANOMA CELLS
Notcovich, Cintia
1
*; Sanchez Crespo, Rodrigo
2
; Grissi, Cecilia
3
;
Delgado, Diana Catherine
3
; Molinari, Beatriz
1
; Ibañez, Irene
3
; Duran, Hebe
1
1
Comisión Nacional de Energía Atómica (CNEA). Argentina.
2
Universidad Nacional de San Martín (UNSAM). Argentina.
3
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Argentina.
* Responsible author, email: notcovich@cnea.gov.ar
Melanoma cells are highly resistant to chemo or radiotherapy. DNA damage agents such as
ionizing radiation induce apoptosis involving RhoB protein. In a great variety of tumors the levels
of this protein decrease along tumor progression. RhoB is considered a tumor suppressor gene
due to its antiproliferative and proapoptotic effect. Considering the aforementioned, the aim of
this study was to characterize the radiobiological response of different human melanoma cell
lines, and to evaluate the possible correlation between RhoB expression, radiosensitivity and
apoptosis. The human melanoma cell lines A375, MELJ and SB2 were gamma-irradiated
(137Cs). Survival curves were obtained by clonogenic assay and fitted to the Linear-Quadratic
(LQ) model. Radiosensitivity was evaluated by surviving fraction at 2 Gy (SF2). Results showed
that MELJ was significantly more radioresistant (SF2=0.71) than A375 and SB2 (0.29 and 0.21
respectively). Expression levels of RhoB, evaluated by western blot, increased in all lines vs.
non-irradiated control. SB2, the most radiosensitive cells, showed a greater induction (p<0.05)
of RhoB. Finally, to study whether RhoB has a radiosensitizing effect, these cell lines were
stably transfected with a wild type RhoB construction, a constituvely active RhoB mutant V14, or
with the empty plasmid as control. For all cell lines higher expression level of this protein was
found in RhoB or V14 transfected cells (p<0.05). Sensitization was evaluated by SF2.
Significant radiosensitization was demonstrated in clones derived from A375 and SB2 (p<0.05),
while for MELJ cells, radio-sensitization was only found in clones overexpressing V14. In
conclusion, the increase of RhoB in melanoma cell lines, either by radiation or transfection has
a radiosensitizing effect. Thus, we propose RhoB modulation as a potential therapeutic tool to
improve the radiation response of radioresistant melanoma.