Retinoids inhibit squamous cell carcinoma growth and intercellular communication.
BACKGROUND
Retinoids have been shown to inhibit the growth of squamous cell carcinoma and other malignancies. They have also been shown to alter gap junctional intercellular communication (GJIC) and the expression of connexins, the protein subunits of gap junctions. We report in this study that the alteration of GJIC by retinoids may be directly related to inhibitory effects on cell growth.


METHODS
SCC-13 cells were treated with all-trans retinoic acid (tRA) and 13-cis retinoic acid (cRA) at 10(-7) and 10(-6) M concentrations in culture. No treatment and ethanol vehicle controls were included for each experiment. Serial cell counts of parallel cultures were performed to determine cell growth. The parachute technique was performed in combination with fluorescence activated cell sorting (FACS) analysis to determine GJIC. Northern and Western blot analysis were performed to assess connexin mRNA and protein expression.


RESULTS
The growth rate was inhibited for cells treated with tRA (10(-6) M) (P < 0.05) and cRA (10(-6) M) (P = 0.068) vs. vehicle control. GJIC was significantly inhibited with both tRA (10(-7) and 10(-6) M) (P < 0.001) and cRA (10(-7) and 10(-6) M) (P < 0.001) at 24, 48, and 96 h as determined by FACS analysis. To correlate GJIC with cell growth, we studied the effect of glycyrrhetinic acid, a known inhibitor of GJIC. Glycyrrhetinic acid also significantly inhibited cell growth (P < 0.05) vs. control. Connexin 26 and connexin 43 mRNA and protein expression were not significantly altered after retinoid treatment.


CONCLUSIONS
Retinoic acids inhibit both cell growth and GJIC in SCC-13 cells. Retinoids may inhibit cell growth through alteration of GJIC in SCC-13 cells.
Rudkin
George H
GH
Plastic Surgery Section, VA Greater Los Angeles Healthcare System, Los Angeles, California 90073, USA.
Carlsen
Brian T
BT
Chung
Chi Y
CY
Huang
Weibiao
W
Ishida
Kenji
K
Anvar
Bardia
B
Yamaguchi
Dean T
DT
Miller
Timothy A
TA
D015152:Blotting, Northern; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000473:pathology* / Q000517:prevention & control; D002450:Cell Communication / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects*; D000072259:Connexin 26; D018031:Connexin 43 / Q000235:genetics; D017630:Connexins / Q000235:genetics; D005434:Flow Cytometry; D017629:Gap Junctions / Q000187:drug effects; D019695:Glycyrrhizic Acid; D015474:Isotretinoin / Q000494:pharmacology; D016015:Logistic Models; D012333:RNA, Messenger / Q000032:analysis; D012176:Retinoids / Q000494:pharmacology* / Q000627:therapeutic use; D012878:Skin Neoplasms / Q000473:pathology*; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D018031:Connexin 43; D017630:Connexins; D012333:RNA, Messenger; D012176:Retinoids; D000072259:Connexin 26; D014212:Tretinoin; D019695:Glycyrrhizic Acid; D015474:Isotretinoin