TY - JOUR
T1 - Diclofenac-induced stimulation of SMCT1 (SLC5A8) in a heterologous expression system
T2 - A RPE specific phenomenon
AU - Ananth, Sudha
AU - Zhuang, Lina
AU - Gopal, Elangovan
AU - Itagaki, Shiro
AU - Ellappan, Babu
AU - Smith, Sylvia B.
AU - Ganapathy, Vadivel
AU - Martin, Pamela
PY - 2010/3/26
Y1 - 2010/3/26
N2 - SMCT1 is a Na+-coupled monocarboxylate transporter expressed in a variety of tissues including kidney, thyroid, small intestine, colon, brain, and retina. We found recently that several non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the activity of SMCT1. Here we evaluated the effect of diclofenac, also a NSAID, on SMCT1. SMCT1 cDNA was expressed heterologously in the human retinal pigment epithelial cell lines HRPE and ARPE-19, the human mammary epithelial cell line MCF7, and in Xenopus laevis oocytes. Transport was monitored by substrate uptake and substrate-induced currents. Na+-dependent uptake/current was considered as SMCT1 activity. The effect of diclofenac was evaluated for specificity, dose-response, and influence on transport kinetics. To study the specificity of the diclofenac effect, we evaluated the influence of this NSAID on the activity of several other cloned transporters in mammalian cells under identical conditions. In contrast to several NSAIDs that inhibited SMCT1, diclofenac stimulated SMCT1 when expressed in HRPE and ARPE-19 cells. The stimulation was marked, ranging from 2- to 5-fold depending on the concentration of diclofenac. The stimulation was associated with an increase in the maximal velocity of the transport system as well as with an increase in substrate affinity. The observed effect on SMCT1 was selective because the activity of several other cloned transporters, when expressed in HRPE cells and studied under identical conditions, was not affected by diclofenac. Interestingly, the stimulatory effect on SMCT1 observed in HRPE and ARPE-19 cells was not evident in MCF7 cells nor in the X. laevis expression system, indicating that SMCT1 was not the direct target for diclofenac. The RPE-specific effect suggests that the target of diclofenac that mediates the stimulatory effect is expressed in RPE cells but not in MCF7 cells or in X. laevis oocytes. Since SMCT1 is a concentrative transporter for metabolically important compounds such as pyruvate, lactate, β-hydroxybutyrate, and nicotinate, the stimulation of its activity by diclofenac in RPE cells has biological and clinical significance.
AB - SMCT1 is a Na+-coupled monocarboxylate transporter expressed in a variety of tissues including kidney, thyroid, small intestine, colon, brain, and retina. We found recently that several non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the activity of SMCT1. Here we evaluated the effect of diclofenac, also a NSAID, on SMCT1. SMCT1 cDNA was expressed heterologously in the human retinal pigment epithelial cell lines HRPE and ARPE-19, the human mammary epithelial cell line MCF7, and in Xenopus laevis oocytes. Transport was monitored by substrate uptake and substrate-induced currents. Na+-dependent uptake/current was considered as SMCT1 activity. The effect of diclofenac was evaluated for specificity, dose-response, and influence on transport kinetics. To study the specificity of the diclofenac effect, we evaluated the influence of this NSAID on the activity of several other cloned transporters in mammalian cells under identical conditions. In contrast to several NSAIDs that inhibited SMCT1, diclofenac stimulated SMCT1 when expressed in HRPE and ARPE-19 cells. The stimulation was marked, ranging from 2- to 5-fold depending on the concentration of diclofenac. The stimulation was associated with an increase in the maximal velocity of the transport system as well as with an increase in substrate affinity. The observed effect on SMCT1 was selective because the activity of several other cloned transporters, when expressed in HRPE cells and studied under identical conditions, was not affected by diclofenac. Interestingly, the stimulatory effect on SMCT1 observed in HRPE and ARPE-19 cells was not evident in MCF7 cells nor in the X. laevis expression system, indicating that SMCT1 was not the direct target for diclofenac. The RPE-specific effect suggests that the target of diclofenac that mediates the stimulatory effect is expressed in RPE cells but not in MCF7 cells or in X. laevis oocytes. Since SMCT1 is a concentrative transporter for metabolically important compounds such as pyruvate, lactate, β-hydroxybutyrate, and nicotinate, the stimulation of its activity by diclofenac in RPE cells has biological and clinical significance.
KW - Diclofenac
KW - NSAIDs
KW - RPE
KW - SLC5A8
KW - SMCT1
UR - http://www.scopus.com/inward/record.url?scp=77949874932&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=77949874932&partnerID=8YFLogxK
U2 - 10.1016/j.bbrc.2010.02.109
DO - 10.1016/j.bbrc.2010.02.109
M3 - Article
C2 - 20178774
AN - SCOPUS:77949874932
SN - 0006-291X
VL - 394
SP - 75
EP - 80
JO - Biochemical and Biophysical Research Communications
JF - Biochemical and Biophysical Research Communications
IS - 1
ER -