The ability of insulin-like growth factor I (IGF-I) to stimulate cartilage matrix synthesis is reduced in aged and osteoarthritic cartilage. Aging and osteoarthritis are associated with an increase in reactive oxygen species, which we hypothesized would interfere with normal IGF-I signaling. We compared IGF-I signaling in normal and osteoarthritic human articular chondrocytes and investi-

We show here that cyclin-dependent kinase 5 (CDK5), a known regulator of migration in neuronal development, plays an important role in prostate cancer motility and metastasis. P35, an activator of CDK5 that is indicative of its activity, is expressed in a panel of human and rat prostate cancer cell lines, and is also expressed in 87.5% of the human metastatic prostate cancers we examined. Blocking of CDK5 activity with a dominant-negative CDK5 construct, small interfering RNA, or roscovitine resulted in changes in the microtubule cytoskeleton, loss of cellular polarity, and loss of motility. Expression of a dominant-negative CDK5 in the highly metastatic Dunning AT6.3 prostate cancer cell line also greatly impaired invasive capacity. CDK5 activity was important for spontaneous metastasis in vivo; xenografts of AT6.3 cells expressing dominant-negative CDK5 had less than onefourth the number of lung metastases exhibited by AT6.3 cells expressing the empty vector. These results show that CDK5 activity controls cell motility and metastatic potential in prostate cancer. (Cancer Res 2006; 66(15): 7509-15)

Sustained activation of the Ras/Raf/MEK/extracellular signal-regulated kinase (ERK) pathway can lead to cell cycle arrest in many cell types. We have found, with human medullary thyroid cancer (MTC) cells, that activated Ras or c-Raf-1 can induce growth arrest by producing and secreting an autocrine-paracrine factor. This protein was purified from cell culture medium conditioned by Raf-activated MTC cells and was identified by mass spectrometry as leukemia inhibitory factor (LIF). LIF expression upon Raf activation and subsequent activation of JAK-STAT3 was also observed in small cell lung carcinoma cells, suggesting that this autocrineparacrine signaling may be a common response to Ras/Raf activation. LIF was sufficient to induce growth arrest and differentiation of MTC cells. This effect was mediated through the gp130/JAK/STAT3 pathway, since anti-gp130 blocking antibody or dominant-negative STAT3 blocked the effects of LIF. Thus, LIF expression provides a novel mechanism allowing Ras/Raf signaling to activate the JAK-STAT3 pathway. In addition to this cell-extrinsic growth inhibitory pathway, we find that the Ras/Raf/MEK/ERK pathway induces an intracellular growth inhibitory signal, independent of the LIF/JAK/STAT3 pathway. Therefore, activation of the Ras/Raf/ MEK/ERK pathway can lead to growth arrest and differentiation via at least two different signaling pathways. This use of multiple pathways may be important for "fail-safe" induction and maintenance of cell cycle arrest.

Kinase activity is known as the key biochemical property of MAPKs. Here, we report that ERK1/2 also utilizes its noncatalytic function to mediate certain signal transductions. Sustained activation of the Raf/MEK/ERK pathway induces growth arrest, accompanied by changes in cell cycle regulators (decreased retinoblastoma phosphorylation, E2F1 down-regulation, and/or p21 CIP1 up-regulation) and cell type-specific changes in morphology and expression of c-Myc or RET in the human tumor lines LNCaP, U251, and TT. Ablation of ERK1/2 by RNA interference abrogated all these effects. However, active site-disabled ERK mutants (ERK1-K71R, ERK2-K52R, and ERK2-D147A), which competitively inhibit activation of endogenous ERK1/2, could not block Raf/MEK-induced growth arrest as well as changes in the cell cycle regulators, although they effectively blocked phosphorylation of the ERK1/2 catalytic activity readouts, p90 RSK and ELK1, as well as the cell type-specific changes. Because this indicated a potential noncatalytic ERK1/2 function, we generated stable lines of the tumor cells in which both ERK1 and ERK2 were significantly knocked down, and we further investigated the possibility using rat-derived kinase-deficient ERK mutants (ERK2-K52R and ERK2-T183A/Y185F) that were not targeted by human small hairpin RNA. Indeed, ERK2-K52R selectively restored Raf-induced growth inhibitory signaling in ERK1/2-depleted cells, as manifested by regained cellular ability to undergo growth arrest and to control the cell cycle regulators without affecting c-Myc and morphology. However, ERK2-T183A/Y185F was less effective, indicating the requirement of TEY site phosphorylation. Our study suggests that functions of ERK1/2 other than its "canonical" kinase activity are also involved in the pathway-mediated growth arrest signaling. ERK12 and its homologue ERK2, the MAPK components of the Raf/MEK/ERK cascade of Ras signaling, are ubiquitously expressed serine/threonine kinases with more than 160 substrates identified to date (1). ERK1/2 interacts with a wide variety of proteins (2, 3). Upon phosphorylation by MEK1/2, the only known activator of ERK1/2, ERK1/2 phosphorylates transcription factors, other kinases, phosphatases, cytoskeletal proteins, scaffolds, receptors, and signaling components that mediate diverse cellular processes. Although kinase activity of ERK1/2 is central in activation or inactivation of these ERK targets, it was also reported that ERK, in an in vitro reaction, can mediate noncatalytic activation of DNA topoisomerase II␣, suggesting that ERK1/2 also has noncatalytic function (4). Nonetheless, the possibility that ERK1/2 has functions other than kinase has not yet been clearly addressed in cells.Many studies have shown that ERK1/2 signaling is pivotal in controlling cell survival and cell cycle progression (5). Constitutive activation of the MAPK cascade is also a central signature of many cancers with dysregulated Ras/Raf signaling (6, 7). Paradoxically, sustained activation of the Ras/Raf pathway induces growth arrest in p...

PURPOSE BRAFV600 mutations are commonly found in melanoma and thyroid cancers and to a lesser degree in other tumor types. Subprotocol H (EAY131-H) of the NCI-MATCH platform trial sought to investigate the selective BRAF inhibitor dabrafenib and the MEK1/2 inhibitor trametinib in patients with solid tumors, lymphomas, or multiple myeloma whose tumors harbored a BRAFV600 mutation. PATIENTS AND METHODS EAY131-H is an open-label, single-arm study. Patients with melanoma, thyroid, or colorectal cancer were excluded; patients with non–small-cell lung cancer were later excluded in an amendment. Patients received dabrafenib 150 mg twice per day and trametinib 2 mg per day continuously until disease progression or intolerable toxicity. The primary end point was centrally assessed objective response rate (ORR); secondary end points included progression-free survival (PFS), 6-month PFS, and overall survival. RESULTS Thirty-five patients were enrolled, and 29 were included in the primary efficacy analysis as prespecified in the protocol. Median age was 59 years, and 45% of the patients had received ≥ 3 lines of therapy. The confirmed ORR was 38% (90% CI, 22.9% to 54.9%) with P < .0001 against a null rate of 5%, and PFS was 11.4 months (90% CI, 8.4 to 16.3 months); responses were seen in 7 distinct tumor types. Seven patients had a duration of response of > 12 months, including 4 patients with a duration of response of > 24 months. An additional 8 patients had a PFS > 6 months. The median overall survival was 28.6 months. Reported adverse events were comparable to those noted in previously reported profiles of dabrafenib and trametinib. CONCLUSION This study met its primary end point, with an ORR of 38% ( P < .0001) in this mixed histology, pretreated cohort. This promising activity warrants additional investigations in BRAFV600-mutated tumors outside of currently approved indications.

b Dysregulated Raf/MEK/extracellular signal-regulated kinase (ERK) signaling, a common hallmark of tumorigenesis, can trigger innate tumor-suppressive mechanisms, which must be inactivated for carcinogenesis to occur. This innate tumor-suppressive signaling may provide a potential therapeutic target. Here we report that mortalin (HSPA9/GRP75/PBP74) is a novel negative regulator of Raf/MEK/ERK and may provide a target for the reactivation of tumor-suppressive signaling of the pathway in cancer. We found that mortalin is present in the MEK1/MEK2 proteome and is upregulated in human melanoma biopsy specimens. In different MEK/ERK-activated cancer cell lines, mortalin depletion induced cell death and growth arrest, which was accompanied by increased p21 CIP1 transcription and MEK/ERK activity. Remarkably, MEK/ERK activity was necessary for mortalin depletion to induce p21 CIP1 expression in B-Raf V600E -transformed cancer cells regardless of their p53 status. In contrast, in cell types exhibiting normal MEK/ERK status, mortalin overexpression suppressed B-Raf V600E -or ⌬Raf-1:ER-induced MEK/ERK activation, p21CIP1 expression, and cell cycle arrest. Other HSP70 family chaperones could not effectively replace mortalin for p21 CIP1 regulation, suggesting a unique role for mortalin. These findings reveal a novel mechanism underlying p21 CIP1 regulation in MEK/ERK-activated cancer and identify mortalin as a molecular switch that mediates the tumor-suppressive versus oncogenic result of dysregulated Raf/MEK/ERK signaling. Our study also demonstrates that p21 CIP1 has dual effects under mortalin-depleted conditions, i.e., mediating cell cycle arrest while limiting cell death.

Discrepancies between planned and delivered movements of multi-leaf collimators (MLCs) are an important source of errors in dose distributions during radiotherapy. In this work we used machine learning techniques to train models to predict these discrepancies, assessed the accuracy of the model predictions, and examined the impact these errors have on quality assurance (QA) procedures and dosimetry. Predictive leaf motion parameters for the models were calculated from the plan files, such as leaf position and velocity, whether the leaf was moving towards or away from the isocenter of the MLC, and many others. Differences in positions between synchronized DICOM-RT planning files and DynaLog files reported during QA delivery were used as a target response for training of the models. The final model is capable of predicting MLC positions during delivery to a high degree of accuracy. For moving MLC leaves, predicted positions were shown to be significantly closer to delivered positions than were planned positions. By incorporating predicted positions into dose calculations in the TPS, increases were shown in gamma passing rates against measured dose distributions recorded during QA delivery. For instance, head and neck plans with 1%/2 mm gamma criteria had an average increase in passing rate of 4.17% (SD = 1.54%). This indicates that the inclusion of predictions during dose calculation leads to a more realistic representation of plan delivery. To assess impact on the patient, dose volumetric histograms (DVH) using delivered positions were calculated for comparison with planned and predicted DVHs. In all cases, predicted dose volumetric parameters were in closer agreement to the delivered parameters than were the planned parameters, particularly for organs at risk on the periphery of the treatment area. By incorporating the predicted positions into the TPS, the treatment planner is given a more realistic view of the dose distribution as it will truly be delivered to the patient.

UDP-glucose pyrophosphorylase (UGPase) is an important enzyme in the metabolism of UDP-glucose, a precursor for the synthesis of carbohydrate cell wall components, such as cellulose and callose. The Arabidopsis thaliana genome contains two putative genes encoding UGPase, AtUGP1 and AtUGP2. These genes are expressed in all organs. In order to determine the role of UGPase in vegetative and reproductive organs, we employed a reverse genetic approach using the T-DNA insertion mutants, atugp1 and atugp2. Despite a significant decrease in UGPase activity in both the atugp1 and atugp2 single mutants, no decrease in normal growth and reproduction was observed. In contrast, the atugp1/atugp2 double mutant displayed drastic growth defects and male sterility. At the reproductive phase, in the anthers of atugp1/atugp2, pollen mother cells developed normally, but callose deposition around microspores was absent. Genes coding for enzymes at the subsequent steps in the cellulose and callose synthesis pathway were also down-regulated in the double mutant. Taken together, these results demonstrate that the AtUGP1 and AtUGP2 genes are functionally redundant and UGPase activity is essential for both vegetative and reproductive phases in Arabidopsis. Importantly, male fertility was not restored in the double knockout mutant by an application of external sucrose, whereas vegetative growth was comparable in size with that of the wild type. In contrast, an application of external UDP-glucose recovered male fertility in the double mutant, suggesting that control of UGPase in carbohydrate metabolism is different in the vegetative phase as compared with the reproductive phase in A. thaliana.