Mammalian mitogen-activated protein kinase pathways are regulated through formation of specific kinase-activator complexes.

Mammalian cells contain at least three signaling systems which are structurally related to the mitogen-activated protein kinase (MAPK) pathway. Growth factors acting through Ras primarily stimulate the Raf/MEK/MAPK cascade of protein kinases. In contrast, many stress-related signals such as heat shock, inflammatory cytokines, and hyperosmolarity induce the MEKK/SEK(MKK4)/SAPK(JNK) and/or the MKK3 or MKK6/p38(hog) pathways. Physiological agonists of these pathway types are either qualitatively or quantitatively distinct, suggesting few common proximal signaling elements, although past studies performed in vitro, or in cells using transient over-expression, reveal interaction between the components of all three pathways. These studies suggest a high degree of cross-talk apparently not seen in vivo. We have examined the possible molecular basis of the differing agonist profiles of these three MAPK pathways. We report preferential association between MAP kinases and their activators in eukaryotic cells. Furthermore, using the yeast 2-hybrid system, we show that association between these components can occur independent of additional eukaryotic proteins. We show that SAPK(JNK) or p38(hog) activation is specifically impaired by co-expression of cognate dominant negative MAP kinase kinase mutants, demonstrating functional specificity at this level. Further divergence and insulation of the stress pathways occurs proximal to the MAPK kinases since activation of the MAPK kinase kinase MEKK results in SAPK(JNK) activation but does not cause p38(hog) phosphorylation. Therefore, in intact cells, the three MAPK pathways may be independently regulated and their components show specificity in their interaction with cognate cascade members. The degree of intermolecular specificity suggests that mammalian MAPK signaling pathways may remain distinct without the need for specific scaffolding proteins to sequester components of individual pathways.

The stress-activated protein kinase pathway mediates cell death following injury induced by cis-platinum, UV irradiation or heat.

BACKGROUND: Stimuli that stress cells, including inflammatory cytokines, ultra-violet irradiation, DNA-damaging chemotherapeutic drugs and heat shock, stimulate a recently identified cytoplasmic signaling system that is structurally related to the mitogen-activated protein kinase pathway. This pathway consists of a cascade of protein kinases including stress-activated protein kinase (SAPK), also termed Jun N-terminal kinase (JNK), and two kinases that activate it, MEKK and SEK/MKK4. Despite rapid progress in delineating the components of this pathway, the cellular consequence of its activation remains to be defined. RESULTS: We have screened cells for defects in SAPK signaling and identified a cell line, previously characterized for its thermotolerance properties, as being more refractive to SAPK activation induced by heat stress than its thermosensitive parental line. Stable expression of dominant inhibiting SEK mutants in thermosensitive parental cells specifically and effectively blocked SAPK activation after heat shock. These lines also became markedly resistant to the cytocidal effects of thermal stress, confirming the phenotype of the thermotolerant line. These cell lines defective in SAPK activation were also resistant to the lethal effects of the DNA-damaging drug cis-platinum. CONCLUSIONS: Experimentally induced stable blockade of SAPK activation in cells with normal thermosensitivity is sufficient to confer resistance to cell death induced by diverse stimuli including heat and the chemotherapeutic agent cis-platinum. These results suggest that activation of the SAPK pathway by diverse cell stressors plays a critical part in mediating the toxicity of these treatments and inducing cell death. SAPK activation in this context could broadly influence cellular response to stress, modulate apoptosis during development or determine the clinical response of tumor cells to cytotoxic therapies.

Cardiac evaluation during physical rehabilitation of the complex medical patient.

Many rehabilitation patients have cardiovascular disease as a primary or secondary diagnosis. Such patients require careful evaluation before institution of vigorous therapeutic exercise and activity regimens. However, conventional exercise tests are often inappropriate due to orthopedic, neurologic, or functional limitations. This article introduces a new method of cardiac assessment, called the Trendscriber Evaluation (TE). The TE uses the Trendscriber, a cardiac telemetry unit which provides a hard-copy single-lead electrocardiogram (SECG) printout and digital heart rate monitor. The TE was developed to assess SECG, hemodynamic, and symptomatic responses during preestablished submaximal levels of activity. Specially trained physical and occupational therapists conduct the evaluation, directing the patient and monitoring vital signs. Results are interpreted by a staff cardiologist. For two years this technique was evaluated for 100 patients in the form of a medical records review. Eighty-nine percent of the patients' TEs identified cardiac abnormalities with heart rhythms, hemodynamic response, or both. Arrhythmia activity not detected on the routine 12-lead electrocardiogram (ECG) was recorded in 49.5% of the TEs performed. Fifty-seven percent of the records revealed activity-related ventricular ectopic activity. Data uncovered by the TE resulted in alteration of medical and/or rehabilitation therapy in 63% of the patients. The review suggests that the TE is a valuable tool in identifying problems related to cardiovascular performance and in providing the health care team with information important for patient management.