Age-related Decline in Mitogen-activated Protein Kinase Activity in Epidermal Growth Factor-stimulated Rat Hepatocytes

Yusen Liu,Kathryn Z Guyton,Myriam Gorospe,Qingbo Xu,Gertrude C Kokkonen,Yolanda D Mock,George S Roth,Nikki J Holbrook

doi:10.1074/jbc.271.7.3604

Yusen Liu, Kathryn Z Guyton + Show 6 more

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https://doi.org/10.1074/jbc.271.7.3604

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Abstract

A number of studies have demonstrated that the proliferative capacity of cells declines with aging. In particular, epidermal growth factor (EGF)-stimulated DNA synthesis is reduced in hepatocytes from aged rats relative to young rats. Growth factor stimulation activates a genetic program in large part regulated by a family of mitogen-activated protein kinases (MAPK) that phosphorylate and thereby activate transcription factors involved in controlling the expression of proliferation-associated genes. In the present study, we compared the activation of the extracellular signal-regulated kinase 2 (ERK2) and c-Jun N-terminal kinase 1 (JNK1) MAPK in EGF-stimulated hepatocytes derived from young (6-month) and aged (24-month) rats. JNK activity was not appreciably altered by EGF treatment of cells from either age group. In contrast, ERK2 was highly activated by EGF treatment, but the magnitude of activation was significantly lower in hepatocytes of aged animals compared to those of young animals (7-fold versus 20-fold, respectively). The reduced ERK2 activity in response to EGF was associated with decreased c-fos and c-jun mRNA expression and lower levels of AP-1 transcription factor DNA binding activity in the aged hepatocytes. Finally, the basal expression of MAPK phosphatase 1, a MAPK-regulated gene involved in regulating MAPK activity, was higher in aged hepatocytes. Taken together, these findings suggest that an alteration in the balance between MAP kinase-phosphatase activities could contribute to the age-related decline in proliferative capacity.

Highlights

A number of studies have demonstrated that the proliferative capacity of cells declines with aging
extracellular signal-regulated kinase 2 (ERK2) was rapidly phosphorylated in response to epidermal growth factor (EGF) treatment, as evidenced by a shift in the mobility of the protein; the slower migrating form appeared within 15 min and persisted up to 45 min post-treatment
AP-1 transcription factor activity is regulated at two different levels in response to growth factor stimulation: phosphorylation of pre-existing and newly synthesized c-Fos and c-Jun proteins and induction of c-fos and c-jun gene expression. Since both mechanisms are dependent on mitogen-activated protein kinases (MAPK) activation (34, 35), we examined the AP-1 DNA binding activity in cell extracts of old and young hepatocytes stimulated with EGF (Fig. 5)

Summary

Introduction

A number of studies have demonstrated that the proliferative capacity of cells declines with aging. The basal expression of MAPK phosphatase 1, a MAPK-regulated gene involved in regulating MAPK activity, was higher in aged hepatocytes Taken together, these findings suggest that an alteration in the balance between MAP kinase-phosphatase activities could contribute to the age-related decline in proliferative capacity. Mitogen-activated protein kinases (MAPKs), which include the extracellular signal-regulated kinases (ERK) and the c-Jun N-terminal kinases (JNK), are important regulatory proteins through which a wide variety of extracellular signals are transduced into intracellular events (1– 6). Both ERKs and JNKs are themselves activated through complex phosphorylation cascades (1, 5, 6), and their activation, in turn, leads to the phos-. Recent studies indicate that its activation is achieved through an alternative signaling cascade involving small GTPases, MEK kinase (MEKK) and the MEK homolog SEK1/MKK4/JNKK (11–17)

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