Correlation between p38 mitogen-activated protein kinase and human telomerase reverse transcriptase in sarcomas

Background One of the major components of telomerase is the human telomerase reverse transcriptase (hTERT) as the catalytic protein. hTERT mRNA expression are reported to be associated with prognosis and tumor progression in several sarcomas. However, there is no clear understanding of the mechanisms of hTERT in human sarcomas. Recent studies have suggested that signals transmitted through p38 mitogen-activated protein kinase (MAPK) can increase or decrease hTERT transcription in human cells. The purpose of this study was to analyse the correlation between p38 MAPK and hTERT in sarcoma samples. Methods We investigated 36 soft tissue malignant fibrous histiocytomas (MFH), 24 liposarcomas (LS) and 9 bone MFH samples for hTERT and p38 MAPK expression. Quantitative detection of hTERT and p38 MAPK was performed by RT-PCR. Results There was a significant positive correlation between the values of hTERT and p38 MAPK in all samples (r = 0.445, p = 0.0001), soft tissue MFH (r = 0.352, p = 0.0352), LS (r = 0.704, p = 0.0001) and bone MFH samples (r = 0.802, p = 0.0093). Patients who had a higher than average expression of p38 MAPK had a significantly worse prognosis than other patients (p = 0.0036). Conclusions p38 MAPK may play a role in up-regulation of hTERT, and therefore, p38 MAPK may be a useful marker in the assessment of hTERT and patients' prognosis in sarcomas.


Background
Telomerase, an enzyme related to cellular immortality, stabilizes telomere length by adding DNA repeats onto telomere ends [1,2]. Many studies have revealed that telomerase activity is expressed in many different types of carcinomas, detected in more than 85% of the human carcinoma samples, and it has been found to be useful as a prognostic indicator [3][4][5]. Telomerase activity is mainly regulated by human telomerase reverse transcriptase (hTERT), which is the catalytic subunit of telomerase [6,7]. Also, hTERT has been significantly detected in many types of sarcoma samples, and previous reports have indicated that hTERT expression is associated with tumor aggressiveness, feature and clinical outcome in sarcomas [8][9][10][11][12][13][14]. Therefore, hTERT may play an important role in telomere maintenance mechanisms in human sarcomas. However, it is notable that thus far, there has been no clear understanding of the mechanisms of hTERT expression especially in sarcomas. p38 is a mitogen-activated protein kinase (MAPK) activated by phosphorylation on serine/threonine residue when cells are exposed to cellular stress, and has a wide variety of biological functions [15][16][17]. Recent studies have suggested that signals transmitted through MAP kinase can increase or decrease hTERT transcription in response to various stimuli, depending on the downstream mediators [18][19][20][21][22]. This study was undertaken to analyze the clinical significance of p38 MAPK and hTERT expression in primary tumor samples from soft tissue malignant fibrous histiocytomas (MFH), liposarcomas (LS) and bone MFH patients. In addition, with the broader aim of discovering regulation factors of hTERT in sarcomas, we investigated whether there is a correlation between hTERT and p38 MAPK.

Patients and tumor samples
A total of 69 (36 soft tissue MFHs, 24 LSs and 9 bone MFHs) sarcoma samples were obtained at the time of surgery, were immediately frozen and stored at -80°C until commencement of our study. Summarized clinical data at the time of last observation are shown in Tables 1, 2 and 3. All patients with these sarcomas were treated with tumor resection and/or chemotherapy between 1988 and 2005. We performed brachytherapy or external radiation therapy following conservative surgery for all soft tissue sarcoma patients who received marginal resection. Chemotherapy comprised of multiagent systemic chemotherapy in metastatic patients. High dose ifosfamide, doxorubicin and/or cisplatin were used. We collected all primary tumor samples by tumor resection or biopsy, and no patients had undergone chemotherapy before surgical specimens were collected. The study was approved by our institutional review board (Dai eki 133, and 263).

Quantification of hTERTand p38 MAPK mRNA expression
Total cellular RNA was extracted using a Rneasy Mini Kit (Qiagen, Valencia, CA), and cDNA was synthesized using 1 μg of total RNA using a Transcriptor First Strand cDNA Synthesis Kit (Roche Applied Science, Mannheim, Germany). Quantitative detection of hTERT mRNA and p38 MAPK was performed with the Light-Cycler TaqMan Master using the LightCycler instrument (Roche Molecular System, Alameda, CA). The primer pairs 5'-CGGAAGAGTGTCTGGAGCAA-3' and 5'-GGATGAAGCGGAGTCTGGA-3' for hTERT, and 5'-ATGCCGAAGATGAACTTTGC-3' and 5'-TCTTATCTGAGTCCAATACAAGCATC-3' for p38 MAPK were used for amplification. PCR used 10 seconds at 95°C, 30 seconds at 60°C and 1 second at 72°C with 45 cycles. Expression of the gene glyceraldehyde-3phosphate dehydrogenase (GAPDH) was also analyzed in each tumor sample as an indicator of RNA quality. A 3 × 10 6 of HeLa cell was used as a positive control. Quantification of mRNA expression was indicated by measuring mRNA expression levels of hTERT or p38 MAPK/mRNA levels of the Hela cell ratio.

Statistical analysis
The cumulative prospective of overall survival was calculated using the method of Kaplan-Meier. Statistical significance of the differences between the survival curves was evaluated using the log-rank test. Pearson's productmoment correlation coefficient (r and p values) was used to study the relationship between p38 MAPK and hTERT. Data are presented as the mean ± SD. In all analyses, a p value of < 0.05 was considered to indicate significance.

Correlation between levels of p38 MAPK and hTERT mRNA expression
There was a significant correlation between the values of p38 MAPK expression and hTERT, with increased p38 MAPK expression with higher hTERT in all samples (r = 0.445, p = 0.0001) ( Figure 1).

Prognostic factors
Patients who had a higher than average expression of p38 MAPK had a significantly worse prognosis (5-year survival rate; 38.1%) than other patients overall (73.8%) (p = 0.0036) ( Figure 2). There were no significant differences in prognosis between patients who had a higher than average expression of hTERT (5-year survival rate: 38.6%) and those who did not (71.1%) (p = 0.0585).

Correlation between levels of p38 MAPK and hTERT mRNA expression
There was a significant correlation between the values of p38 MAPK expression and hTERT, with increased p38 MAPK expression with higher hTERT in soft tissue MFH samples (r = 0.352, p = 0.0352) ( Figure 3).

Prognostic factors
There were no significant differences in prognosis between patients who had a higher than average expression of p38 MAPK (5-year survival rate: 41.7%) and those who did not (65.0%) (p = 0.213). There were no significant differences in prognosis between patients who had a higher than average expression of hTERT (41.7%) and those who did not (62.7%) (p = 0.610).

Correlation between levels of p38 MAPK and hTERT mRNA expression
There was a significant correlation between the values of p38 MAPK expression and hTERT, with increased p38 MAPK expression with higher hTERT in LS samples (r = 0.704, p = 0.0001) (Figure 4).

Prognostic factors
Patients who had a higher than average expression of p38 MAPK (5-year survival rate: 50.0%) had a

Correlation between levels of p38 MAPK and hTERT mRNA expression
There was a significant correlation between the values of p38 MAPK expression and hTERT, with increased p38 MAPK expression with higher hTERT (r = 0.802, p = 0.0093) ( Figure 5).

Prognostic factors
Patients who had a higher than average expression of p38 MAPK (5-year survival rate: 0%) had a worse prognosis than other patients (66.7%), but did not reach significant differences (p = 0.202). There were no significant differences in prognosis between patients who had a higher than average expression of hTERT (33.3%) and those who did not (50.0%) (p = 0.904).

Discussion
hTERT is the catalytic telomerase subunit component that copies a template region of its functional RNA subunit to the end of the telomere. In terms of carcinomas, hTERT mRNA expression and telomerase activity are closely associated, and quantification of hTERT mRNA has been reported as an alternative to the measure of telomerase activity [7,25,26]. Also, in sarcomas, the correlation between telomerase activity and hTERT has been reported [9,10,27]. However, in contrast, previous reports maintained that hTERT expression does not correlate to telomerase activity [12,23], and hTERT mRNA expression was only studied in the absence of detectable telomerase activity on sarcomas [8,12,27,28].
There is no clear understanding of the discordance between hTERT and telomerase activity in sarcomas [23,29]. Recently, the presence of telomerase activity and alternative lengthening of telomeres (ALT) in several sarcomas was examined extensively, and these studies indicate a positive correlation between the telomere maintenance mechanism and tumor aggressiveness in several sarcoma types [29]. Furthermore, a positive correlation between hTERT and tumor aggressiveness in several sarcomas has been reported [8][9][10][11][12][13][14]. Therefore, it could be necessary to analyze hTERT, in order to elucidate the telomere maintenance mechanisms and the tumorigenesis of sarcomas. The predominence of large numbers of protein kinases involved in signal cascades following genotoxic stress is the p38 MAPK [30]. p38 MAPK is shown to induce a wide variety of intracellular responses, with roles in tumorigenesis, cell-cycle regulation, development, inflammation and apoptosis [15][16][17]. Recent studies have suggested that signals transmitted through MAP kinase can regulate hTERT transcription. Epidermal growth factor (EGF) affects the up-regulation of hTERT transcription through the MAP kinase cascades [20]. E26 transformation-specific (Ets) transcription factors, downstream of the mitogen signaling pathways of MAP kinase, regulates hTERT [31]. p38 MAPK may play an important role in the activation of the hTERT promoter by the upstream stimulatory factor (USF) in tumor cells [32]. In the present study, there was a significant positive correlation between the values of p38 MAPK expression and hTERT, with increased p38 MAPK expression with higher hTERT in sarcoma samples. This is the first report to show a correlation between the levels of hTERT mRNA expression and the levels of p38 MAPK in human sarcomas, and these results may suggest that p38 MAPK plays a role in up-regulation of hTERT in soft tissue MFH, liposarcomas, and bone MFH, while we do not have a clear understanding if some factor regulates both p38 MAPK and hTERT expression.
Recent studies have demonstrated that p38 MAPK has diverse roles in the pathogenesis of several cancers and have shown that they are also involved in regulating other functions including the differentiation and proliferation of various cell types [33]. The p38 MAPK pathway is most frequently associated with a tumor suppressor function, based on its negative regulation of proliferation and survival of cells [33,34]. However, contradictory effects have been observed, a fact that points to the pathway playing a positive role in cell-cycle progression in some carcinoma cells [35][36][37]. In terms of sarcoma cells, inhibition of p38 MAPK activity rescues the antitumor agent fenretinide-mediated cell death in Ewing's sarcoma family of tumors [38], and inhibition of p38 signals results showing a significant reduction in      [39], which suggests that p38 MAPK may play an important role in tumorigenesis in these sarcomas. In the clinical setting, p38 MAPK expression correlates to poor prognosis (p = 0.0036) in overall patients; of high expression of p38 MAPK, indicating the likelihood of a poor outcome and may indicate a positive role of p38 MAPK in tumor proliferation and aggressiveness, in patients with sarcomas. In terms of bone and soft tissue MFH, there were no significant differences in prognosis between patients who had a higher than average expression of p38 MAPK and those who did not. However, patients who had above average p38 (5-year survival rate: soft tissue MFH; 41.7%, bone MFH; 0%) had a worse prognosis than other patients (5-year survival rate: soft tissue MFH; 65.0%, bone MFH; 66.7%), but did not reach significant differences. These results may be due to small numbers of patients. Patients who had a higher than average expression of p38 MAPK (5-year survival rate: 50.0%) had a significantly worse prognosis than other patients (88.9%) (p = 0.0448) in LS patients. Therefore, high expression of p38 MAPK may correlate with a worse prognosis especially for LS patients.

Conclusions
p38 MAPK may be a useful marker in the assessment of hTERT and prognosis. Given that more than 80% of sarcomas express p38 MAPK and hTERT, elucidation of the pathways and target genes of p38 MAPK in sarcomas will yield additional understandings into the pathogenesis of several sarcomas and may lead to novel therapeutic strategies for their treatment.