Submitted on February 12, 2007
Accepted on June 8, 2007
A 78kD Glucose-Regulated Protein Is Involved in Decrease of Interleukin-6 Secretion by Lead Treatment from Astrocytes
Yongchang Qian1*, Ying Zheng1, Deanna Weber1, and Evelyn Tiffany-Castiglioni1
1 Integrative Biosciences, Texas A&M University, College Station, Texas, United States
* To whom correspondence should be addressed. E-mail: yqian{at}cvm.tamu.edu.
Interleukin-6 (IL-6) is a cytokine produced mainly by microglia and astrocytes and plays a pleiotropic role in the central nervous system (CNS). In this study, we cloned rat IL-6 cDNA into an enhanced green fluorescent protein (EGFP) or a red fluorescent protein (DsRed2) vector and rat 78 kD glucose-regulated protein (GRP78) cDNA into an EGFP vector to construct IL-6-EGFP, IL-6-DeRed2, and GRP78-EGFP chimeras for the investigation of the mechanism of IL-6 secretion from astrocytes. Data showed that constructed IL-6-EGFP and IL-6-DsRed2 chimeras retained the secretory property and the secretion of IL-6-EGFP from astrocytes could be attenuated by GRP78 depletion with dsRNAi. Co-expression of IL-6-DsRed2 and dysfunctional GRP78-EGFP abolished IL-6-DsRed2 secretion and two chimeric proteins co-localized inside living astrocytes. Co-immunoprecipitation analysis indicated that IL-6 and GRP78 resided in the same complex. Data further revealed that IL-6-EGFP secretion from astrocytes was blocked by the heavy metal lead (Pb) in a concentration-dependent manner. Analysis of Pb interaction with protein on a Pb-affinity column demonstrated that Pb bound to GRP78 but failed to bind to IL-6. Therefore, these data suggest that IL-6-EGFP or IL-6-DsRed2 chimera can be used as imaging probes to study IL-6 secretion from living cells, GRP78 is involved in IL-6 secretion from astrocytes, and heavy metal Pb can block IL-6 secretion from astrocytes via targeting GRP78.
