Parathyroid hormone inhibits c-Jun N-terminal kinase activity in rat osteoblastic cells by a protein kinase...

Area of Science:

• Cell Biology
• Molecular Biology
• Endocrinology

Background:

• Parathyroid hormone (PTH) activates dual signaling cascades, protein kinase A (PKA) and protein kinase C (PKC), in osteoblastic cells.
• PTH's effect on extracellular signal-regulated kinases (ERKs) is dose-dependent, but its regulation of other mitogen-activated protein kinase (MAPK) family members, like c-Jun-NH(2)-terminal kinase (JNK), remains unclear.
• JNK is typically activated by cellular stress and cytokines, playing a crucial role in transcription factor regulation.

Purpose of the Study:

• To investigate the effect of PTH on JNK activity in osteoblastic cells.
• To determine if PTH regulates other members of the MAPK family, specifically JNK.
• To elucidate the signaling pathway through which PTH influences JNK activity.

Main Methods:

• Treatment of UMR 106-01 cells and rat calvarial osteoblasts with PTH (10(-8) M).
• Treatment with N-terminal PTH peptides selective for PKA activation.
• Treatment with 8-bromo-cAMP to activate PKA.
• Assay of JNK activity and upstream components of the JNK cascade, including stress-activated protein kinase/extracellular signal-related kinase kinase 1/MAPK kinase 4 and MAPK/extracellular signal-related kinase kinase kinase 1.

Main Results:

• PTH treatment significantly inhibited high basal JNK activity in osteoblastic cells.
• N-terminal PTH peptides and 8-bromo-cAMP also resulted in the inhibition of JNK activity.
• PTH treatment led to the inhibition of upstream signaling components of the JNK cascade, specifically SAPK/ERK kinase 1 and MAPK/ERK kinase 1.

Conclusions:

• PTH inhibits high basal JNK activity in osteoblastic cells.
• The PKA signaling cascade is responsible for PTH-mediated inhibition of JNK.
• PTH influences the JNK pathway through its upstream activators via PKA activation.