Protein Kinase A Activation Down-Regulates, Whereas Extracellular Signal-Regulated Kinase Activation Up-Regulates σ-1 Receptors in B-104 Cells: Implication for Neuroplasticity

Abstract

The -1 receptor (Sig-1R) can bind psychostimulants and was shown to be up-regulated in the brain of methamphetamine self-administering rats. Up-regulation of Sig-1Rs has been implicated in neuroplasticity. However, the mechanism(s) whereby Sig-1Rs are up-regulated by psychostimulants is unknown. Here, we employed a neuroblastoma cell line B-104, devoid of dopamine receptors and transporter, and examined the effects of psychostimulants as well as cAMP on the expression of Sig-1Rs in this cell line, with a specific goal to identify signal transduction pathway(s) that may regulate Sig-1R expression. Chronic treatments of B-104 cells with physiological concentrations of cocaine or methamphetamine failed to alter the expression of Sig-1Rs. N 6 ,2Ј-O-Dibutyryl-cAMP (dBcAMP), when used at 0.5 mM, caused a down-regulation of Sig-1Rs that could be blocked by a protein kinase A (PKA) inhibitor, N- [2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-89). However, dB-cAMP, when used at 2 mM, caused an up-regulation of Sig-1Rs that was insensitive to the H-89 blockade but was partially blocked by an extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase inhibitor PD98059 (2Ј-amino-3Ј-methoxyflavone). Furthermore, 2 mM dB-cAMP induced an ERK phosphorylation lasting at least 90 min, at which time the phosphorylation caused by 0.5 mM dB-cAMP had already diminished. PD98059, applied 90 min after addition of 2 mM dB-cAMP, attenuated the Sig-1R up-regulation. Our results indicate that cAMP is bimodal in regulating Sig-1R expression: a downregulation via PKA and an up-regulation via ERK. Results also suggest that psychostimulants may manipulate the cAMP-PKA-Sig-1R and/or the cAMP-ERK-Sig-1R pathways to achieve a neuroplasticity that favors addictive behaviors.The -1 receptor (Sig-1R) is a unique intracellular nonopioid binding site with nano-to low-micromolar affinities for diverse classes of drugs including benzomorphans, antidepressants, neuroleptics, steroid hormones including progesterone, and psychostimulants such as cocaine and methamphetamine (Sharkey et al., 1988;Su et al., 1988;Snyder and Largent, 1989;Quirion et al., 1992;Nguyen et al., 2005).Sig-1Rs exist in the central and peripheral nervous systems where they modulate neurotransmitter release and cell excitability via ion channels (Monnet et al., 1990;Hayashi and Su, 2001;Aydar et al., 2002;Nuwayhid and Werling, 2003). Behavioral studies implicated Sig-1Rs in higher ordered brain functions including mood and learning and memory (Maurice et al., 2001;Meunier et al., 2004).Recently, a number of studies suggested that psychostimulant-induced behaviors involve an up-regulation of Sig-1Rs. Ujike et al. (1996) demonstrated that cocaine-induced locomotor sensitization was cross-sensitized to the Sig-1R agonist 3-(3-hydroxyphenyl)-N-(1-propyl)piperidine and that the sensitization could be suppressed by a Sig-1R antagonist,

Regulation of σ-1 Receptors and Endoplasmic Reticulum Chaperones in the Brain of Methamphetamine Self-Administering Rats

“…Thus, the present results reveal the olfactory bulb to be a potentially important brain region for studying the role of -1 receptors in methamphetamine self-administration and perhaps the brain reward system in general. Our results with ERK (specifically ERK1) being activated while PKA (specifically PKA RII␣) is down-regulated in the olfactory bulb are consistent with our previous report showing that in B-104 cells ERK activation or PKA inactivation causes an increase in -1 receptors (Cormaci et al, 2007). However, it is not presently known how the interplay between the ERK and PKA might affect levels of -1 receptors in the ventral tegmental area or substantia nigra.…”

“…Mizoguchi et al (2004) found that activation of ERK1 via D1Rs was associated with methamphetamine-induced conditioned place preference. We reported previously that the activation of ERKs up-regulated -1 receptors (Cormaci et al, 2007). We found in the present study that ERK1 is activated in the olfactory bulb of methamphetamine self-administering rats but not in yoked methamphetamine rats that receive the drug passively.…”

“…Although a splice variant of -1 receptors is reported in lymphocytes (Ganapathy et al, 1999), we could not detect any variants in our samples from rat brains. Together with -1 receptors, three ER chaperones (BiP, calreticulin, and cyclophilin B) and two kinases (ERK and PKA) were also examined in this study because they are related to the action of -1 receptors (Stefanski et al, 2004;Cormaci et al, 2007) or methamphetamine (Jayanthi et al, 2004). Representative Western blotting of the chaperones and the kinases in the chosen brain region are shown in Fig.…”

“…In this study, we also examined the densities of ERK and PKA in the three groups of rats from the self-administration experiment because the activation of ERK or PKA has been previously shown by us to increase or decrease, respectively, the level of -1 receptors in B-104 cells (Cormaci et al, 2007). Regarding ERK, the degree of phosphorylation (i.e., the activation) of two types of ERK, ERK1 (p44) and ERK2 (p42), was examined.…”

Role of the σRs for Development of Medications

“…σ1Rs are intracellular chaperone proteins that translocate from their primary endoplasmic reticulum localization to different subcellular compartments upon agonist actions, and regulate ion channels and G-protein-coupled-receptor signaling [12][13][14]. In fact, reports have implicated σ1Rs in various biological functions, and drugs acting at these receptors have been studied for therapeutic effects in psychiatric disorders including substance abuse,…”