Effects of the protein tyrosine kinase inhibitor, herbimycin A, on prolactin gene expression in GH3 and 235-1 pituitary tumor cells

Exploration of the Effects of TGF-β Pathway-Based Pituitary Tumor of Rats on GH3 Cell Line after Intervention with Different Concentrations of TGZ

The effect of the TGF-β pathway-based pituitary tumor of rats on the GH3 cell line after intervention with different concentrations of troglitazone (TGZ) is explored. The CH3 cell line of 24 clean male SD rats with pituitary adenoma is selected. The cells are divided into a blank contrast set and an experimental set. The experimental set is divided into different TGZ concentration sets, including 1 × 10-3 TGZ set, 1 × 10-4 TGZ set, and 1 × 10-5 TGZ set. The cell proliferation is detected by the CCK-8 method, the protein expressions of CD147, TGF-β1, and MMP-9 are detected by the western blot method, and the relative mRNA expressions of CD147, TGF-β1, and MMP-9 are detected by the qRT-PCR method. The expression levels of CD147, TGF-β1, and MMP-9 in CH3 cells of pituitary adenoma rats are notoriously lower, while the expression of CD147, TGF-31, and MMP-9 could be reduced by TGZ acting on the GH3 cell line. The specific mechanism of action of this effect on the invasive ability of GH3 cell lines is multifaceted, suggesting that peroxisome proliferator activator-receptor (PPAR-γ) agonists have good clinical application prospects in tumor therapy and can provide new targets and approaches for tumor drug therapy.

Regulation of the Ca2+ channel α2δ-1 subunit expression by epidermal growth factor via the ERK/ELK-1 signaling pathway

Voltage-gated Ca²⁺ (Ca_V) channels are expressed in endocrine cells where they contribute to hormone secretion. Diverse chemical messengers, including epidermal growth factor (EGF), are known to affect the expression of Ca_V channels. Previous studies have shown that EGF increases Ca²⁺ currents in GH3 pituitary cells by increasing the number of high voltage-activated (HVA) Ca_V channels at the cell membrane, which results in enhanced prolactin (PRL) secretion. However, little is known regarding the mechanisms underlying this regulation. Here, we show that EGF actually increases the expression of the Ca_Vα₂δ-1 subunit, a key molecular component of HVA channels. The analysis of the gene promoter encoding Ca_Vα₂δ-1 (CACNA2D1) revealed binding sites for transcription factors activated by the Ras/Raf/MEK/ERK signaling cascade. Chromatin immunoprecipitation and site-directed mutagenesis showed that ELK-1 is crucial for the transcriptional regulation of CACNA2D1 in response to EGF. Furthermore, we found that EGF increases the membrane expression of Ca_Vα₂δ-1 and that ELK-1 overexpression increases HVA current density, whereas ELK-1 knockdown decreases the functional expression of the channels. Hormone release assays revealed that Ca_Vα₂δ-1 overexpression increases PRL secretion. These results suggest a mechanism for how EGF, by activating the Ras/Raf/MEK/ERK/ELK-1 pathway, may influence the expression of HVA channels and the secretory behavior of pituitary cells.

Tyrosine kinase inhibitors in preclinical development

Due to the limited efficacy of cytotoxic chemotherapy in the treatment of advanced malignancy and its excessive toxicity precluding its use in chemoprevention, new therapeutic and preventive strategies have been sought. One of the most interesting of these new approaches is the manipulation of signal transduction pathways. Among the approaches being considered to eventuate such a strategy is the inhibition of autophosphorylation, a critical first step in the signal transduction pathways of many cell surface receptor tyrosine kinases, as well as of non-receptor tyrosine kinases. This article is intended to review those tyrosine kinase inhibitors that are currently in preclinical development, for which there are data to support consideration for their use in chemoprevention or cancer treatment. We will focus upon those agents that have received attention in the past several years.

Differential influences of gender and physiological status on calcium dynamics and prolactin gene expression in rat mammotropes

The rate of prolactin (PRL) secretion is influenced by the gender and physiological state of an animal, but little is known about the mechanisms involved. In the present study, we assessed possible contributions of Ca2+ dynamics and PRL gene expression to these differences. This was accomplished by monitoring spontaneous [Ca2+]i changes and PRL promotor-driven reporter activity in pituitary cultures derived from rats comprising a broad spectrum of PRL secretory capacities: male, cycling female, and lactating rats. We found that Ca2+ oscillatory activity exhibited a rank order of lactating > cycling females > males, consistent with the reported secretory capacities of mammotropes from these sources. Interestingly, we observed that the basal level of PRL promotor-driven reporter activity was the same for all three models, but that mammotropes from males were the most responsive to stimulation of PRL gene expression by elevation of [Ca2+]i. Collectively, our findings reveal gender- and state-specific differences in Ca2+ dynamics and induction of PRL gene expression. These likely contribute to reported differences in secretory capacity.