Prognostic significance of PU.1 in follicular lymphoma

Expression of Transcription Factor PU.1 in Stromal Cells as a Prognostic Marker in Non-Small Cell Lung Cancer

Transcription factor PU.1 is involved in hematopoiesis and is expressed in various cells of the inflammatory infiltrate of the tumor stroma, mainly in macrophages. The expression of PU.1 in 100 samples of non-small cell lung cancer was analyzed by the immunohistochemical method. The number of PU.1+ cells did not correlate with clinical and morphological parameters of the tumors. However, increased number of PU.1+ cells significantly correlated with favorable prognosis in adenocarcinoma and poor prognosis in squamous cell carcinoma. Thus, transcription factor PU.1 can serve as a stromal prognostic marker of non-small cell lung cancer depending on the histological type of the tumor.

Transcription factor PU.1 is involved in the progression of glioma

Glioma is a severe disease of the central nervous system. Although previous studies have identified the important role of the immune response in association with tumor intervention, it is still unknown whether PU.1, a transcription factor known for its role in myeloid differentiation and immune responses, is involved in the progression of glioma. In the present study, we found a significant increase in SPI1, the gene that encodes PU.1, in samples from patients with glioma. Through genotype-phenotype association analysis several candidate factors that may mediate the role of PU.1 in glioma were identified. To further validate the association between PU.1 and glioma we found that the expression of BTK, a potential target of PU.1, was also upregulated in patients with glioma. We also demonstrated that various biological pathways could be involved in PU.1-associated glioma by analyzing these potential targets in the Reactome database. These results provide evidence that PU.1 could serve a role in the progress of glioma through its transcriptional targets in multiple signaling pathways. Therefore, in addition to its role in hematopoietic linage development and leukemia, PU.1 appears to be involved in the regulation of glioma and potentially in other malignant cancers.

Oncogenic microRNA-155 and its target PU.1: an integrative gene expression study in six of the most prevalent lymphomas

The transcription factor PU.1 and its inhibitory microRNA-155 (miR-155) are important regulators of B-cell differentiation. PU.1 downregulation coupled with oncogenic miR-155 upregulation has been reported in lymphoid malignancies; however, these data have not been studied across different subtypes in relation to clinical outcomes. We studied expression of miR-155 and PU.1 in the six most prevalent human B-cell lymphomas (n = 131) including aggressive (DLBCL, HL, MCL) and indolent (B-CLL/SLL, MZL, FL) types. Levels of miR-155 and PU.1 inversely correlated in DLBCL, B-CLL/SLL, and FL tumor tissues. In HL tissues, an exceptionally high level of miR-155 was found in patients with unfavorable responses to first-line therapy and those who had shorter survival times. PU.1 downregulation was noted in B-CLL/SLL samples positive for the adverse prognostic markers CD38 and ZAP-70. Upregulation of miR-155 and downregulation of PU.1 expression are integral aspects of lymphoma biology that could mark aggressive behavior of some, but not all, lymphoma types.

Clinical characteristics and early treatment outcomes of follicular lymphoma in young adults

Follicular lymphoma (FL) in young adults (YA, <40 years old) is uncommon, and the clinical characteristics and outcomes of this group are not well defined. We conducted a retrospective database review of 427 patients with newly diagnosed FL aged 65 years or less registered at Princess Margaret Cancer Centre between 1995 and 2010. YA (n = 61) and those 40-65 (n = 366) were compared with regards to clinical stage at diagnosis, FL International Prognostic Index (FLIPI) score, and the following clinical outcomes: time to second treatment, cause-specific survival (CSS) and overall survival (OS). At diagnosis, stage and FLIPI score were similar, as were the proportion of patients requiring therapy (YA 75% versus older adults 71%). Median follow-up was 8.1 years. Time to second therapy was similar in both age groups (5-year probability 23% YA versus 27% older adults; Gray's P-value = 0.76). Ten-year OS was significantly higher for YA (87% versus older adults 72%; P = 0.029). On multivariate analysis, age <40 years, low FLIPI score and observation as initial management were favourable prognostic factors for OS and CSS. We conclude that YA with FL have a favourable prognosis compared to older patients; whether this reflects competing mortality risks or age-related differences in lymphoma biology warrants further investigation.

A PU.1 suppressive target gene, metallothionein 1G, inhibits retinoic acid-induced NB4 cell differentiation

We recently revealed that myeloid master regulator SPI1/PU.1 directly represses metallothionein (MT) 1G through its epigenetic activity of PU.1, but the functions of MT1G in myeloid differentiation remain unknown. To clarify this, we established MT1G-overexpressing acute promyelocytic leukemia NB4 (NB4MTOE) cells, and investigated whether MT1G functionally contributes to all-trans retinoic acid (ATRA)-induced NB4 cell differentiation. Real-time PCR analyses demonstrated that the inductions of CD11b and CD11c and reductions in myeloperoxidase and c-myc by ATRA were significantly attenuated in NB4MTOE cells. Morphological examination revealed that the percentages of differentiated cells induced by ATRA were reduced in NB4MTOE cells. Since G1 arrest is a hallmark of ATRA-induced NB4 cell differentiation, we observed a decrease in G1 accumulation, as well as decreases in p21WAF1/CIP1 and cyclin D1 inductions, by ATRA in NB4MTOE cells. Nitroblue tetrazolium (NBT) reduction assays revealed that the proportions of NBT-positive cells were decreased in NB4MTOE cells in the presence of ATRA. Microarray analyses showed that the changes in expression of several myeloid differentiation-related genes (GATA2, azurocidin 1, pyrroline-5-carboxylate reductase 1, matrix metallopeptidase -8, S100 calcium-binding protein A12, neutrophil cytosolic factor 2 and oncostatin M) induced by ATRA were disturbed in NB4MTOE cells. Collectively, overexpression of MT1G inhibits the proper differentiation of myeloid cells.

Molecular functions of metallothionein and its role in hematological malignancies

Metallothionein (MT) was reported to be a potential negative regulator of apoptosis, and various reports have suggested that it may play roles in carcinogenesis and drug resistance, in at least a portion of cancer cells. The author summarizes the current understanding of the molecular functions of MT for tumor cell growth and drug resistance. These activities are regulated through intracellular metal ion modulation and free radical scavenging. Compared with analyses of solid tumors, few studies have analyzed the roles of MT in hematological malignancies. This review mainly describes the functions of MT in hematopoietic cells. Furthermore, through expression analyses of leukemias and lymphomas, the roles of MT in the biology of these diseases are particularly focused upon.

Improved demonstration of immunohistochemical prognostic markers for survival in follicular lymphoma cells

Follicular lymphoma (FL) is one of the most common forms of the low-grade non-Hodgkin's lymphoma in adults, with a characteristic translocation, t(14;18)(q32;q21) that deregulates the expression of the BCL2 gene. The clinical course of FL patients is variable, whereby a subset of patients survive for long periods even without relapses, whereas the majority have frequent relapses with shorter survival. We have analyzed a series of 186 FLs, studying the correlation between clinical outcome and the tumor cell expression of a set of immunohistochemical markers, using an automated procedure for tissue microarrays to reduce the subjectivity of scoring. The results identified several markers associated with differences in overall survival (OS) in univariate analyses, such as Cyclin E, Mdm2, CD10, p21, IgD, Bcl-xL, CD30, and E2F6. Cases with a higher level of expression of Cyclin E, Mdm2, p21, IgD, Bcl-xL, CD30, and E2F6 were associated with a significantly shorter OS. On the other hand, strong CD10 expression was linked to a significantly better outcome. A Cox model was then constructed, integrating the Follicular Lymphoma International Prognostic Index (FLIPI) score and a restricted selection of three immunohistochemical markers: Cyclin E, Mdm2, and CD10 expression. A potentially useful finding is that the integrated FLIPI plus immunohistochemical model can be used to identify a subset of 26 patients (almost 20% of the total series), with a survival probability of 100% at 5 years. This not only confirms that a group of FL cases may have a very good clinical course, but also indicates that this group can be identified using this integrated clinical and immunohistochemical approach.

Pathology, pathogenesis and molecular genetics of follicular NHL

Follicular lymphoma (FL) is a germinal centre-derived indolent B-cell lymphoma representing the second most common Non Hodgkin lymphoma in the Western world. This chapter focuses on the pathology of FL and summarizes the current knowledge about genetic and molecular features that are relevant for the pathogenesis of this neoplasm. The translocation t(14;18) is present in approximately 90% of FL leading to the upregulation of the anti-apoptotic protein BCL2, that may constitute a promising molecular target for therapeutic approaches. FL lacking the t(14;18) also exist, and B-cells carrying the t(14;18) can be detected in a subset of healthy individuals. In addition to the t(14;18), secondary genetic alterations are present in most FL and, more recently, deeper insights into the methylation and microRNA expression patterns in the tumour cells have been gained. The tumour microenvironment appears to be particularly important for the biology and the clinical course of FL.

Prognostic Factors in Follicular Lymphoma

Follicular lymphoma (FL) is one of the most common types of non-Hodgkin's lymphoma. It is usually diagnosed at an advanced stage, for which many treatment options exist, however, no curative standard therapy has been identified. The outcome is highly variable with a median survival of approximately 10 years. The life expectancy of patients with FL has been extended with the use of rituximab, a monoclonal antibody targeting the CD20 antigen on FL cells, but there remains a group of patients who fail to respond to chemoimmunotherapy and die early of their disease. Transformation of FL to an aggressive histology is an important event with high morbidity and mortality. The Follicular Lymphoma International Prognostic Index has become the clinically useful prognostic tool, but gives only a rough estimate of expected outcome. There is a need for useful biomarkers for prediction of the disease course of single patients to individualize therapy, especially in the new era of chemoimmunotherapy.

Metallothionein-1 isoforms and vimentin are direct PU.1 downstream target genes in leukemia cells

PU.1 is a key transcription factor for hematopoiesis and plays important roles in various hematological malignancies. To clarify the molecular function of PU.1, we initially tried to identify bona fide target genes regulated by PU.1. Dual microarrays were employed for this study to compare PU.1-knockdown K562 cells (K562PU.1KD) stably expressing PU.1 short inhibitory RNAs versus control cells and PU.1-overexpressing K562 cells (K562PU.1OE) versus control cells. In these analyses, we found that several genes, including metallothionein (MT)-1 isoforms (MT-1G and MT-1A) and vimentin (VIM), were markedly induced while Jun dimerization protein (JDP) 2 was suppressed in K562PU.1KD cells. Furthermore, the mRNA expressions of the MT-1 and VIM genes were inversely correlated and the mRNA expression of JDP2 was positively correlated with PU.1 mRNA expression in 43 primary acute myeloid leukemia specimens (MT-1G: R = -0.50, p < 0.001; MT-1A: R = -0.58, p < 0.0005; VIM: R = -0.39, p < 0.01; and JDP2: R = 0.30, p < 0.05). Next, we analyzed the regulation of the MT-1 and VIM genes. We observed increased associations of acetylated histones H3 and H4 with the promoters of these genes in K562PU.1KD cells. Sequence analyses of the regions approximately 1 kb upstream from the transcription start sites of these genes revealed numerous CpG sites, which are potential targets for DNA methylation. Chromatin immunoprecipitation assays revealed that methyl CpG-binding protein 2 (MeCP2) and PU.1 bound to the CpG-rich regions in the MT-1 and VIM promoters. Bisulfite sequencing analyses of the PU.1-bound regions of these promoters revealed that the proportions of methylated CpG sites were tightly related to the PU.1 expression levels.

Identification of annexin 1 as a PU.1 target gene in leukemia cells

To identify PU.1 downstream target genes, we first established PU.1-knockdown K562 (K562PU.1KD) cells expressing reduced levels of PU.1 by stably transfected PU.1 siRNAs. From microarray analysis, we found that several genes including annexin 1 were markedly induced in K562PU.1KD cells. Annexin 1 is a calcium- and phospholipid-binding protein and increased expression leads to the constitutive activation of extracellular signal-regulated kinase (ERK). Consistent with this, we observed constitutive activation of ERK in K562PU.1KD cells. Furthermore, we revealed the mRNA expression of annexin 1 was negatively correlated with PU.1 mRNA expression in 43 primary AML specimens (R=-0.31, p<0.042).

High numbers of tumor-associated macrophages have an adverse prognostic value that can be circumvented by rituximab in patients with follicular lymphoma enrolled onto the GELA-GOELAMS FL-2000 trial

PURPOSE

High amounts of intratumoral macrophages have been shown to correlate with poor prognosis in patients with follicular lymphoma (FL) treated with chemotherapy without rituximab. We tried to establish whether intratumoral macrophage count (MC) definitely is able to predict the outcome of FL patients in the rituximab era.

PATIENTS AND METHODS

We analyzed immunohistochemical CD68 expression in 194 FL patients from the FL-2000 trial, randomly assigned to receive cyclophosphamide, doxorubicin, etoposide, prednisolone, and interferon (CHVP-I) or rituximab plus CHVP-I. Immunohistochemistry was performed on paraffin sections using anti-CD68 KP1 antibody, and stained macrophages were scored on high-power field (hpf) in either intrafollicular (IF) or extrafollicular (EF) areas.

RESULTS

For IF MC, the best cutoff point was estimated at 10 macrophages/hpf. Low IF MC was significantly associated with a better event-free survival (EFS; P = .011). However, this effect was observed only in the CHVP-I arm (P = .012) and not in the rituximab plus CHVP-I arm. Using a cutoff of 15 IF MC, we found no significant association with EFS. For EF MC, fewer than 22 macrophages/hpf were associated with better EFS in the CHVP-I arm (P = .02) but not in the rituximab plus CHVP-I arm.

CONCLUSION

These results show that MC can predict outcome of FL patients and that rituximab is able to circumvent the unfavorable outcome associated with high MC.

Grading of follicular lymphoma: comparison of routine histology with immunohistochemistry

CONTEXT

Follicular lymphoma (FL) grading is based on the average number of large transformed cells in 10 neoplastic follicles at x40 high-power field (x10-40 high-power field) examination (grade 1, 0-5 centroblasts per high-power field; grade 2, 6-15 centroblasts per high-power field; grade 3, >15 centroblasts per high-power field).

OBJECTIVE

Since there may be significant interobserver variability, we analyzed the usefulness of immunohistochemical stains in grading FLs more reliably.

DESIGN

Forty-three FLs initially graded by World Health Organization criteria (grade 1, 12; grade 2, 18; grade 3, 13) were reviewed and stained with CD3, CD20, Ki-67, CD30, CD68, PAX-5, and BCL-6. Retrospective review was performed for the average number of large cells, of large lymphoid cells, of large cells staining with CD3, CD20, BCL-6 (40 cases), and PAX-5, and of all cells staining with CD68, Ki-67, and CD30.

RESULTS

By histologic review, 8 of 43 FLs had a significant grade change (4 cases upgraded and 4 cases downgraded). CD3 and CD30 stained only 0 to 3 large cells and 0 to 3 cells, respectively, in neoplastic follicles. CD68+ cells represented the large nonlymphoid cells. Increasing FL grades demonstrated increases in Ki-67+ cells. The original grade showed substantial agreement with CD20 and moderate agreement with PAX-5 and BCL-6. The original histologic grade agreed with immunohistochemical-based grade using 2 or more antibodies in 5 of 8 discordant cases (4 by CD20 or BCL-6 and PAX-5; 1 by CD20, PAX-5, and BCL-6).

CONCLUSIONS

Interobserver variability of histologic FL grading may be significant; we showed low-end "substantial agreement." Immunohistochemical stains (ie, CD20, PAX-5, and BCL-6) may more reliably determine the number of large transformed cells in neoplastic follicles; Ki-67 staining correlates with higher FL grades. Immunohistochemical stains may be evaluated in clinical trials of FL patients to determine prognostic significance.

Optimal Use of Prognostic Factors in Non-Hodgkin Lymphoma

The management of non-Hodgkin lymphoma is complicated by wide heterogeneity within recognized subtypes. Patients with supposedly similar diagnoses can have remarkably varied clinical presentations, molecular profiles and clinical outcomes. Reliable prognostic markers could allow the identification of patient subsets that may benefit from alternate approaches. Historically, a large number of clinical and molecular prognostic factors have been elucidated. However, the recent introduction of new therapies such as monoclonal antibodies has revolutionized treatment practices and greatly improved outcomes. This has called into question the value of previously recognized prognostic factors that need to be revalidated in the era of immunochemotherapy. It would appear that the commonly used clinical indices (IPI and FLIPI) retain predictive capacity, although they may have limited ability to identify a very poor outcome group. Currently there are no molecular markers that have been revalidated and shown to retain significance in the setting of current treatment practices for diffuse large B-cell lymphoma or follicular lymphoma. The biologic insights provided by molecular studies should allow for more targeted therapies to be developed, which will increase treatment choice and the possibility of tailored therapy in the future. It is imperative that future steps forward be made in the context of well-designed clinical trials with prospective correlative studies of clinical and biologic markers. This will allow us to continuously assess outcome predictors in the context of treatment change and to rationally design tailored treatment algorithms.