subject: The Role Of Pd98059 In The Formation Of Osteoclast Like Cells [print this page] INTRODUCTION INTRODUCTION
MEK1/2 are the most essential components of the Ras activated MAPK pathway. They are dual specific kinases and play a significant role in activation of the downstream targets like ERK1/2. PD98059 acts as a specific inhibitor to MEK1 and MEK2 enzymes at a concentration of 4 M and 50 M, respectively. A cell contains many other related dual specific enzymes and kinases which are closely related to MEK1 and MEK2. However this inhibitor is very specific in its action and does not affect these enzymes.
PD98059: ACTION ON OA INDUCED CELL DEATH
Okadaic acid or OA is a protein phosphatase inhibitor and its effect was studied on hippocampal neuron cultures. It was found that OA caused a significant damage to these culture cells in a dose dependent manner. ERK1 and ERK2 that is p44/42(mapk) kinases were rapidly phosphorylated at their tyrosine residues. This phosphorylation was found to be reduced by the introduction of the inhibitor, PD98059. This inhibitor could reverse the cell death induced by Okadaic acid [1].
PD98059: HELPS IN THE STUDY OF PHOSPHORYLATION OF NEUROFILAMENT PROTEINS
Neurofilament proteins of mammals like NF-M and NF-H remain in a highly phosphorylated state within the axons. The carboxy terminal tail domains of the NF-H and NF-M contain a number of lys-ser-pro (KSP) repeats. The extent of their phosphorylaion determines their functionality. To identify the exact kinase which phophorylates these repeats a synthetic protein was designed. PD98059 helped in identifying that ERK2 was actually required for the phosphorylation of these repeats. ERK2 was in turn phosphorylated by MEK. The kinase enzymes ERK1 and ERK2 play an essential role in the growth of neuritis and their branching. This conclusion was based on the finding that PD98059 inhibited the activation ofNF-H,NF-M proteins by phosphorylation. PD 98059 also inhibited MAP protein which is also known as microtubule-associated protein within primary hippocampal cells of rat [2].
PD98059: HELPS IN THE FORMATION OF OSTEOCLAST LIKE CELLS
The formation of bone involves continuous remodeling. It involves both bone formation and bone resorption and a perfect balance between these two mechanisms is maintained by the process of homeostasis. If bone resorption does not take place in a balanced way it leads to osteoporosis and osteopetrosis. Osteoclassts are the multinucleated cells which are involved in this process. RANKL or receptor activator of nuclear factor kappa B ligand belongs to the TNF family and induces the process of osteoclastogenesis in an osteoblast stimulated manner. Upon activation by TNF the bone cells produce cytokines. The membranes of the stromal cells express RANKL protein. The completely formed osteoclasts express the RANK protein and the precursors of these cells express the receptor known as RANKL [3] [4]. RANK protein interacts with (TRAF) 2 and TRAF 6 further leading to the activation of MAPK enzymes. PD98059 has helped in finding out that MAPKs are involved in the osteoclast formation. PD98059 enhances the differentiation of RAW264.7 cells into osteoclasts. However the inhibitor of p38 suppresses this process [5]
CONCLUSION
In a nut shell PD98059 has helped in the study of the MAPK pathway. It plays a significant role in the differentiation of RAW264.7 cells into bone cells known as osteoclasts.
REFERENCES
1. Runden E, Seglen PO, et al. Regional selective neuronal degeneration after protein phosphatase inhibition in hippocampal slice cultures: evidence for a MAP kinase-dependent mechanism. J Neurosci 1998 Sep 15; 18(18):7296-305.
2. Veeranna,AminND, et al. Mitogen-activated protein kinases (Erk1,2) phosphorylate Lys-Ser-Pro (KSP) repeats in neurofilament proteins NF-H and NF-M. J Neurosci 1998 Jun 1; 18(11):4008-21.
3. Li J, Sarosi I, et al. RANK is the intrinsic hematopoietic cell surface receptor that controls osteoclastogenesis and regulation of bone mass and calcium metabolism. PNAS 2000 Feb 15; 97(4): 1566-1571.
4. Hsu H, Lacey DL, et al. Tumor necrosis factor receptor family member RANK mediates osteoclast differentiation and activation induced by osteoprotegerin ligand. PNAS 1999 Mar 30; 96(7): 3540-3545.
5. Hotokezaka H, Sakai E, et al. U0126 and PD98059, Specific Inhibitors of MEK, Accelerate Differentiation of RAW264.7 Cells into Osteoclast-like Cells. The Journal of Biological Chemistry 2002 Dec 6; 277: 47366-47372.
