Targeted next generation sequencing identifies clinically actionable mutations in patients with melanoma

Somatic sequencing of cancers has produced new insight into tumorigenesis, tumor heterogeneity, and disease progression, but the vast majority of genetic events identified are of indeterminate clinical significance. Here, we describe a NextGen sequencing approach to fully analyzing 248 genes, including all those of known clinical significance in melanoma. This strategy features solution capture of DNA followed by multiplexed, high-throughput sequencing and was evaluated in 31 melanoma cell lines and 18 tumor tissues from patients with metastatic melanoma. Mutations in melanoma cell lines correlated with their sensitivity to corresponding small molecule inhibitors, confirming, for example, lapatinib sensitivity in ERBB4 mutant lines and identifying a novel activating mutation of BRAF. The latter event would not have been identified by clinical sequencing and was associated with responsiveness to a BRAF kinase inhibitor. This approach identified focal copy number changes of PTEN not found by standard methods, such as comparative genomic hybridization (CGH). Actionable mutations were found in 89% of the tumor tissues analyzed, 56% of which would not be identified by standard-of-care approaches. This work shows that targeted sequencing is an attractive approach for clinical use in melanoma.

Mechanisms of chromosomal instability in melanoma

A systems biology approach was applied to investigate the mechanisms of chromosomal instability in melanoma cell lines. Chromosomal instability was quantified using array comparative genomic hybridization to identify somatic copy number alterations (deletions and duplications). Primary human melanocytes displayed an average of 8.5 alterations per cell primarily representing known polymorphisms. Melanoma cell lines displayed 25 to 131 alterations per cell, with an average of 68, indicative of chromosomal instability. Copy number alterations included approximately equal numbers of deletions and duplications with greater numbers of hemizygous (-1,+1) alterations than homozygous (-2,+2). Melanoma oncogenes, such as BRAF and MITF, and tumor suppressor genes, such as CDKN2A/B and PTEN, were included in these alterations. Duplications and deletions were functional as there were significant correlations between DNA copy number and mRNA expression for these genes. Spectral karyotype analysis of three lines confirmed extensive chromosomal instability with polyploidy, aneuploidy, deletions, duplications, and chromosome rearrangements. Bioinformatic analysis identified a signature of gene expression that was correlated with chromosomal instability but this signature provided no clues to the mechanisms of instability. The signature failed to generate a significant (P = 0.105) prediction of melanoma progression in a separate dataset. Chromosomal instability was not correlated with elements of DNA damage response (DDR) such as radiosensitivity, nucleotide excision repair, expression of the DDR biomarkers γH2AX and P-CHEK2, nor G1 or G2 checkpoint function. Chromosomal instability in melanoma cell lines appears to influence gene function but it is not simply explained by alterations in the system of DDR.

Development of DNA damage response signaling biomarkers using automated, quantitative image analysis

The DNA damage response (DDR) coordinates DNA repair with cell cycle checkpoints to ameliorate or mitigate the pathological effects of DNA damage. Automated quantitative analysis (AQUA) and Tissue Studio are commercial technologies that use digitized immunofluorescence microscopy images to quantify antigen expression in defined tissue compartments. Because DDR is commonly activated in cancer and may reflect genetic instability within the lesion, a method to quantify DDR in cancer offers potential diagnostic and/or prognostic value. In this study, both AQUA and Tissue Studio algorithms were used to quantify the DDR in radiation-damaged skin fibroblasts, melanoma cell lines, moles, and primary and metastatic melanomas. Digital image analysis results for three markers of DDR (γH2AX, P-ATM, P-Chk2) correlated with immunoblot data for irradiated fibroblasts, whereas only γH2AX and P-Chk2 correlated with immunoblot data in melanoma cell lines. Melanoma cell lines displayed substantial variation in γH2AX and P-Chk2 expression, and P-Chk2 expression was significantly correlated with radioresistance. Moles, primary melanomas, and melanoma metastases in brain, lung and liver displayed substantial variation in γH2AX expression, similar to that observed in melanoma cell lines. Automated digital analysis of immunofluorescent images stained for DDR biomarkers may be useful for predicting tumor response to radiation and chemotherapy.

MERTK receptor tyrosine kinase is a therapeutic target in melanoma

Metastatic melanoma is one of the most aggressive forms of cutaneous cancers. Although recent therapeutic advances have prolonged patient survival, the prognosis remains dismal. C-MER proto-oncogene tyrosine kinase (MERTK) is a receptor tyrosine kinase with oncogenic properties that is often overexpressed or activated in various malignancies. Using both protein immunohistochemistry and microarray analyses, we demonstrate that MERTK expression correlates with disease progression. MERTK expression was highest in metastatic melanomas, followed by primary melanomas, while the lowest expression was observed in nevi. Additionally, over half of melanoma cell lines overexpressed MERTK compared with normal human melanocytes; however, overexpression did not correlate with mutations in BRAF or RAS. Stimulation of melanoma cells with the MERTK ligand GAS6 resulted in the activation of several downstream signaling pathways including MAPK/ERK, PI3K/AKT, and JAK/STAT. MERTK inhibition via shRNA reduced MERTK-mediated downstream signaling, reduced colony formation by up to 59%, and diminished tumor volume by 60% in a human melanoma murine xenograft model. Treatment of melanoma cells with UNC1062, a novel MERTK-selective small-molecule tyrosine kinase inhibitor, reduced activation of MERTK-mediated downstream signaling, induced apoptosis in culture, reduced colony formation in soft agar, and inhibited invasion of melanoma cells. This work establishes MERTK as a therapeutic target in melanoma and provides a rationale for the continued development of MERTK-targeted therapies.

Phase I study and biomarker analysis of lapatinib and concurrent radiation for locally advanced breast cancer

PURPOSE

This phase I study assessed the toxicity and safety of combining daily lapatinib with radiation therapy. Sequential tumor biopsies were obtained to evaluate changes in biomarkers, such as epidermal growth factor receptor (EGFR) and human EGFR-2 (HER2) signaling pathways.

METHODS

Eligibility for this dose-escalation study included unresectable and locally recurrent or chemotherapy-refractory and locally advanced breast cancer, and adequate organ function. Patients underwent three serial biopsies: at baseline, after 1 week of lapatinib alone, and after 1 week of lapatinib and radiation. Endpoints included determination of toxicity, maximum tolerated dose, and analysis of the effect of lapatinib with or without radiation on EGFR and HER2 signaling pathways by immunohistochemistry.

RESULTS

Doses of lapatinib up to 1,500 mg/day were well tolerated. Toxicity of grade 3 or more was limited to radiation dermatitis and pain. Out of 19 patients treated, in field responses per response evaluation criteria in solid tumors criteria were complete in four patients and partial in six patients. Serial biopsies were obtained in 16 patients with no complications. Total Her2 was relatively unchanged while phospho-Her2, phospho-Akt, and phospho-ERK showed variable responses to both lapatinib alone and dual therapy with lapatinib and radiation.

CONCLUSIONS

The combination of lapatinib and radiation was well tolerated in this patient cohort. Overall local response rates were comparable to those reported in other studies in this patient population. Biopsies were safely performed at all time points. Inhibition of HER2 and downstream signaling pathways was identified, although no strong correlation with response was seen.

A prognostic signature of defective p53-dependent G1 checkpoint function in melanoma cell lines

Melanoma cell lines and normal human melanocytes (NHM) were assayed for p53-dependent G1 checkpoint response to ionizing radiation (IR)-induced DNA damage. Sixty-six percent of melanoma cell lines displayed a defective G1 checkpoint. Checkpoint function was correlated with sensitivity to IR with checkpoint-defective lines being radio-resistant. Microarray analysis identified 316 probes whose expression was correlated with G1 checkpoint function in melanoma lines (P≤0.007) including p53 transactivation targets CDKN1A, DDB2, and RRM2B. The 316 probe list predicted G1 checkpoint function of the melanoma lines with 86% accuracy using a binary analysis and 91% accuracy using a continuous analysis. When applied to microarray data from primary melanomas, the 316 probe list was prognostic of 4-yr distant metastasis-free survival. Thus, p53 function, radio-sensitivity, and metastatic spread may be estimated in melanomas from a signature of gene expression.

Melanoma cells show a heterogeneous range of sensitivity to ionizing radiation and are radiosensitized by inhibition of B-RAF with PLX-4032

PURPOSE

To assess the relative radiosensitivities of a large collection of melanoma cell lines and to determine whether pharmacologic inhibition of mutant B-RAF with PLX-4032 can radiosensitize B-Raf+ melanoma cells.

MATERIALS AND METHODS

A large collection of melanoma cell lines (n=37) were treated with 0-8Gy IR and clonogenic survival assays used to generate survival curves to rank relative radiosensitivities among the cell lines. The ability of a B-RAF inhibitor, PLX-4032, to radiosensitize highly radioresistant B-Raf+ cells was also assessed by clonogenic cell survival and spheroid invasion assays and the effects of treatment on the cell cycle assessed by FACS.

RESULTS

Melanoma cell lines displayed a very large, heterogeneous range of SF2 values (1.002-0.053) with a mean of 0.51. Cell lines with surviving fractions of 0.29 or less at SF2 and SF4 were observed at a high frequency of 18.9% and 70.2%, respectively. Treatment of B-Raf+ cells with the B-RAF inhibitor PLX-4032 in combination with radiation provided enhanced inhibition of both colony formation and invasion, and radiosensitized cells through an increase in G(1) arrest.

CONCLUSIONS

Our data suggest that melanomas are not uniformly radioresistant with a significant subset displaying inherent radiosensitivity. Pharmacologic inhibition of B-RAF with PLX-4032 effectively radiosensitized B-Raf+ melanoma cells suggesting that this combination approach could provide improved radiotherapeutic response in B-Raf+ melanoma patients.

Similar nucleotide excision repair capacity in melanocytes and melanoma cells

Sunlight UV exposure produces DNA photoproducts in skin that are repaired solely by nucleotide excision repair in humans. A significant fraction of melanomas are thought to result from UV-induced DNA damage that escapes repair; however, little evidence is available about the functional capacity of normal human melanocytes, malignant melanoma cells, and metastatic melanoma cells to repair UV-induced photoproducts in DNA. In this study, we measured nucleotide excision repair in both normal melanocytes and a panel of melanoma cell lines. Our results show that in 11 of 12 melanoma cell lines tested, UV photoproduct repair occurred as efficiently as in primary melanocytes. Importantly, repair capacity was not affected by mutation in the N-RAS or B-RAF oncogenes, nor was a difference observed between a highly metastatic melanoma cell line (A375SM) or its parental line (A375P). Lastly, we found that although p53 status contributed to photoproduct removal efficiency, its role did not seem to be mediated by enhanced expression or activity of DNA binding protein DDB2. We concluded that melanoma cells retain capacity for nucleotide excision repair, the loss of which probably does not commonly contribute to melanoma progression.

Lapatinib in combination with radiation diminishes tumor regrowth in HER2+ and basal-like/EGFR+ breast tumor xenografts

PURPOSE

To determine whether lapatinib, a dual epidermal growth factor receptor (EGFR)/HER2 kinase inhibitor, can radiosensitize EGFR+ or HER2+ breast cancer xenografts.

METHODS AND MATERIALS

Mice bearing xenografts of basal-like/EGFR+ SUM149 and HER2+ SUM225 breast cancer cells were treated with lapatinib and fractionated radiotherapy and tumor growth inhibition correlated with alterations in ERK1 and AKT activation by immunohistochemistry.

RESULTS

Basal-like/EGFR+ SUM149 breast cancer tumors were completely resistant to treatment with lapatinib alone but highly growth impaired with lapatinib plus radiotherapy, exhibiting an enhancement ratio average of 2.75 and a fractional tumor product ratio average of 2.20 during the study period. In contrast, HER2+ SUM225 breast cancer tumors were highly responsive to treatment with lapatinib alone and yielded a relatively lower enhancement ratio average of 1.25 during the study period with lapatinib plus radiotherapy. Durable tumor control in the HER2+ SUM225 model was more effective with the combination treatment than either lapatinib or radiotherapy alone. Immunohistochemical analyses demonstrated that radiosensitization by lapatinib correlated with ERK1/2 inhibition in the EGFR+ SUM149 model and with AKT inhibition in the HER2+ SUM225 model.

CONCLUSION

Our data suggest that lapatinib combined with fractionated radiotherapy may be useful against EGFR+ and HER2+ breast cancers and that inhibition of downstream signaling to ERK1/2 and AKT correlates with sensitization in EGFR+ and HER2+ cells, respectively.

Radiosensitization of epidermal growth factor receptor/HER2-positive pancreatic cancer is mediated by inhibition of Akt independent of ras mutational status

PURPOSE

Epidermal growth factor receptor (EGFR) family members (e.g., EGFR, HER2, HER3, and HER4) are commonly overexpressed in pancreatic cancer. We investigated the effects of inhibition of EGFR/HER2 signaling on pancreatic cancer to elucidate the role(s) of EGFR/HER2 in radiosensitization and to provide evidence in support of further clinical investigations.

EXPERIMENTAL DESIGN

Expression of EGFR family members in pancreatic cancer lines was assessed by quantitative reverse transcription-PCR. Cell growth inhibition was determined by MTS assay. The effects of inhibition of EGFR family receptors and downstream signaling pathways on in vitro radiosensitivity were evaluated using clonogenic assays. Growth delay was used to evaluate the effects of nelfinavir on in vivo tumor radiosensitivity.

RESULTS

Lapatinib inhibited cell growth in four pancreatic cancer cell lines, but radiosensitized only wild-type K-ras-expressing T3M4 cells. Akt activation was blocked in a wild-type K-ras cell line, whereas constitutive phosphorylation of Akt and extracellular signal-regulated kinase (ERK) was seen in lines expressing mutant K-ras. Overexpression of constitutively active K-ras (G12V) abrogated lapatinib-mediated inhibition of both Akt phosphorylation and radiosensitization. Inhibition of MAP/ERK kinase/ERK signaling with U0126 had no effect on radiosensitization, whereas inhibition of activated Akt with LY294002 (enhancement ratio, 1.2-1.8) or nelfinavir (enhancement ratio, 1.2-1.4) radiosensitized cells regardless of K-ras mutation status. Oral nelfinavir administration to mice bearing mutant K-ras-containing Capan-2 xenografts resulted in a greater than additive increase in radiation-mediated tumor growth delay (synergy assessment ratio of 1.5).

CONCLUSIONS

Inhibition of EGFR/HER2 enhances radiosensitivity in wild-type K-ras pancreatic cancer. Nelfinavir, and other phosphoinositide 3-kinase/Akt inhibitors, are effective pancreatic radiosensitizers regardless of K-ras mutation status.

Abstract B73: Lapatinib-mediated radiosensitization of EGFR+/basal breast cancer correlates withERK inhibition in vivo and requires MEK/ERK inhibition in vitro

To determine whether the dual EGFR/HER2 kinase inhibitor lapatinib can radiosensitize EGFR+ breast cancer in vivo, mice bearing xenografts of basal-like/EGFR+ SUM149 breast cancer cells were treated with lapatinib and fractionated radiation therapy over a 10 d period and tumor growth inhibition determined and correlated with changes in activation of downstream signaling to ERK1/2 and AKT by immunohistochemistry. Basal-like/EGFR+ SUM149 breast cancer tumors were completely resistant to treatment with lapatinib alone but highly growth impaired with lapatinib + radiation exhibiting an enhancement ratio average of 2.75 and a fractional tumor product ratio average of 2.06 over the duration of the study. Immunohistochemical analysis demonstrated that radiosensitization by lapatinib correlated with inhibition of ERK1/2 but not AKT. In vitro analysis of other basal breast cancers consistently demonstrated a loss of radiation induced MEK1/2 inhibition with lapatinib treatment. Treatment of the SUM102 basal-like/EGFR+ cell line with the MEK inhibitor CI1040 resulted in radiosensitization at levels similar to that seen with lapatinib alone. Furthermore, constitutive activation of RAF in SUM102 cells abolished the ability of lapatinib to radiosensitize these cells and resulted in enhanced radioresistance relative to parental cells. Collectively, this work demonstrates that lapatinib radiosensitizes EGFR+/basal-like breast cancer both in vitro and in vivo in a MEK/ERK dependent manner, and suggests that lapatinib in combination with fractionated radiation therapy may provide an effective treatment option for breast cancers of this subtype.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B73.

Mechanism of lapatinib-mediated radiosensitization of breast cancer cells is primarily by inhibition of the Raf>MEK>ERK mitogen-activated protein kinase cascade and radiosensitization of lapatinib-resistant cells restored by direct inhibition of MEK

BACKGROUND AND PURPOSE

We recently showed that lapatinib, an EGFR/HER2 inhibitor, radiosensitized breast cancer cells of the basal and HER2+ subtypes. The purpose of this study was to identify the downstream signaling pathways responsible for lapatinib-mediated radiosensitization in breast cancer.

MATERIALS AND METHODS

Response of EGFR downstream signaling pathways was assessed by Western blot and clonogenic cell survival assays in breast tumor cells after irradiation (5Gy), lapatinib, CI-1040, or combined treatment.

RESULTS

In SUM102 cells, an EGFR+ basal breast cancer cell line, exposure to ionizing radiation elicited strong activation of ERK1/2 and JNK, which was blocked by lapatinib, and weak/no activation of p38, AKT or STAT3. Direct inhibition of MEK1 with CI-1040 resulted in 95% inhibition of surviving colonies when combined with radiation while inhibition of JNK with SP600125 had no effect. Lapatinib-mediated radiosensitization of SUM102 cells was completely abrogated with expression of constitutively active Raf. Treatment of lapatinib-resistant SUM185 cells with CI-1040 restored radiosensitization with 45% fewer surviving colonies when combined with radiation.

CONCLUSIONS

These data suggest that radiosensitization by lapatinib is mediated largely through inhibition of MEK/ERK and that direct inhibition of this pathway may provide an additional avenue of radiosensitization in EGFR+ or HER2+ breast cancers.

CD200 is induced by ERK and is a potential therapeutic target in melanoma

Immune-mediated antitumor responses occur in patients with metastatic melanoma (MM), and therapies designed to augment such responses are clinically beneficial. Despite the immunogenicity of melanoma, immunomodulatory therapies fail in the majority of patients with MM. An inability of DCs to sufficiently activate effector cells may, in part, underlie this failure of the antitumor response seen in most patients. In this work, we show that mutation of N-RAS or B-RAF, signature genetic lesions present in most MMs, potently induced the expression of cell-surface CD200, a repressor of DC function. Employing 2 independent, genome-wide microarray analyses, we identified CD200 as a highly dynamic, downstream target of RAS/RAF/MEK/ERK activation in melanoma. CD200 protein was similarly overexpressed in human melanoma cell lines and primary tumors. CD200 mRNA expression correlated with progression and was higher in melanoma than in other solid tumors or acute leukemia. Melanoma cell lines expressing endogenous CD200 repressed primary T cell activation by DCs, while knockdown of CD200 by shRNA abrogated this immunosuppressive effect. These data indicate that in addition to its effects on growth, survival, and motility, ERK activation in MM attenuates a host antitumor immune response, implicating CD200 and its interaction with the CD200 receptor as a potential therapeutic target for MM.

Context-dependent roles of mutant B-Raf signaling in melanoma and colorectal carcinoma cell growth

Mutational activation of Ras and a key downstream effector of Ras, the B-Raf serine/threonine kinase, has been observed in melanomas and colorectal carcinomas. These observations suggest that inhibition of B-Raf activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase kinase (MEK) and the extracellular signal-regulated kinase MAPK cascade may be an effective approach for the treatment of RAS and B-RAF mutation-positive melanomas and colon carcinomas. Although recent studies with interfering RNA (RNAi) and pharmacologic inhibitors support a critical role for B-Raf signaling in melanoma growth, whether mutant B-Raf has an equivalent role in promoting colorectal carcinoma growth has not been determined. In the present study, we used both RNAi and pharmacologic approaches to further assess the role of B-Raf activation in the growth of human melanomas and additionally determined if a similar role for mutant B-Raf is seen for colorectal carcinoma cell lines. We observed that RNAi suppression of mutant B-Raf(V600E) expression strongly suppressed the anchorage-dependent growth of B-RAF mutation-positive melanoma, but not colorectal carcinoma, cells. However, the anchorage-independent and tumorigenic growth of B-RAF mutation-positive colorectal carcinomas was dependent on mutant B-Raf function. Finally, pharmacologic inhibition of MEK and Raf was highly effective at inhibiting the growth of B-RAF mutation-positive melanomas and colorectal carcinoma cells, whereas inhibitors of other protein kinases activated by Ras (AKT, c-Jun NH(2)-terminal kinase, and p38 MAPK) were less effective. Our observations suggest that Raf and MEK inhibitors may be effective for the treatment of B-RAF mutation-positive colorectal carcinomas as well as melanomas.

Defective cell cycle checkpoint functions in melanoma are associated with altered patterns of gene expression

Defects in DNA damage responses may underlie genetic instability and malignant progression in melanoma. Cultures of normal human melanocytes (NHMs) and melanoma lines were analyzed to determine whether global patterns of gene expression could predict the efficacy of DNA damage cell cycle checkpoints that arrest growth and suppress genetic instability. NHMs displayed effective G1 and G2 checkpoint responses to ionizing radiation-induced DNA damage. A majority of melanoma cell lines (11/16) displayed significant quantitative defects in one or both checkpoints. Melanomas with B-RAF mutations as a class displayed a significant defect in DNA damage G2 checkpoint function. In contrast the epithelial-like subtype of melanomas with wild-type N-RAS and B-RAF alleles displayed an effective G2 checkpoint but a significant defect in G1 checkpoint function. RNA expression profiling revealed that melanoma lines with defects in the DNA damage G1 checkpoint displayed reduced expression of p53 transcriptional targets, such as CDKN1A and DDB2, and enhanced expression of proliferation-associated genes, such as CDC7 and GEMININ. A Bayesian analysis tool was more accurate than significance analysis of microarrays for predicting checkpoint function using a leave-one-out method. The results suggest that defects in DNA damage checkpoints may be recognized in melanomas through analysis of gene expression.

Lack of Extracellular Signal-Regulated Kinase Mitogen-Activated Protein Kinase Signaling Shows a New Type of Melanoma

The majority of human melanomas harbor activating mutations of either N-RAS or its downstream effector B-RAF, which cause activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase and the ERK MAPK cascade. The melanoma-relevant effectors of ERK activation, however, are largely unknown. In this work, we show that increased ERK activation correlates strongly with mutational status of N-RAS or B-RAF in 21 melanoma cell lines. Melanoma lines that were wild-type for RAS/RAF showed low levels of ERK activation comparable with primary human melanocytes. Through supervised analysis of RNA expression profiles, we identified 82 genes, including TWIST1, HIF1alpha, and IL-8, which correlated with ERK activation across the panel of cell lines and which decreased with pharmacologic inhibition of ERK activity, suggesting that they are ERK transcriptional targets in melanoma. Additionally, lines lacking mutations of N-RAS and B-RAF were molecularly distinct and characterized by p53 inactivation, reduced ERK activity, and increased expression of epithelial markers. Analysis of primary human melanomas by tissue microarray confirmed a high correlation among expression of these epithelial markers in a heterogeneous sample of 570 primary human tumors, suggesting that a significant frequency of primary melanomas is of this "epithelial-like" subtype. These results show a molecularly distinct melanoma subtype that does not require ERK activation or epithelial-mesenchymal transformation for progression.

Use of retrovirus expression of interfering RNA to determine the contribution of activated K-Ras and ras effector expression to human tumor cell growth

Cancer is a multistep genetic process that includes mutational activation of oncogenes and inactivation of tumor suppressor genes. The Ras oncogenes are the most frequently mutated oncogenes in human cancers (30%), with a high frequency associated with cancers of the lung, colon, and pancreas. Mutational activation of Ras is commonly an early event in the development of these cancers. Thus, whether mutated Ras is required for tumor maintenance and what aspects of the complex malignant phenotype might be promoted by mutated Ras are issues that remain unresolved for these and other human cancers. The recent development of interfering RNA to selectively impair expression of mutated Ras provides a powerful approach to begin to resolve these issues. In this chapter, we describe the use of retrovirus-based RNA interference approaches to study the functions of Ras and Ras effectors (Raf, RalA, RalB, and Tiam1) in the growth of pancreatic carcinoma and other human tumor cell lines. Finally, we also compare the use of constitutive and inducible shRNA expression vectors for analyses of mutant Ras function.

RKIP downregulates B-Raf kinase activity in melanoma cancer cells

The Raf-MEK-ERK protein kinase cascade is a highly conserved signaling pathway that is pivotal in relaying environmental cues from the cell surface to the nucleus. Three Raf isoforms, which share great sequence and structure similarities, have been identified in mammalian cells. We have previously identified Raf kinase inhibitor protein (RKIP) as a negative regulator of the Raf-MEK-ERK signaling pathway by specifically binding to the Raf-1 isoform. We show here that RKIP also antagonizes kinase activity of the B-Raf isoform. Yeast two-hybrid and coimmunoprecipitation experiments indicated that RKIP specifically interacted with B-Raf. Ectopic expression of RKIP antagonized the kinase activity of B-Raf. We showed that the effects of RKIP on B-Raf functions were independent of its known inhibitory action on Raf-1. The expression levels of RKIP in melanoma cancer cell lines are low relative to primary melanocytes. Forced expression of RKIP partially reverted the oncogenic B-Raf kinase-transformed melanoma cancer cell line SK-Mel-28. The low expression of RKIP and its antagonistic action on B-Raf suggests that RKIP may play an important role in melanoma turmorgenesis.

Ras-mediated loss of the pro-apoptotic response protein Par-4 is mediated by DNA hypermethylation through Raf-independent and Raf-dependent signaling cascades in epithelial cells

The apoptosis-promoting protein Par-4 has been shown to be down-regulated in Ras-transformed NIH 3T3 fibroblasts through the Raf/MEK/ERK MAPK pathway. Because mutations of the ras gene are most often found in tumors of epithelial origin, we explored the signaling pathways utilized by oncogenic Ras to down-regulate Par-4 in RIE-1 and rat ovarian surface epithelial (ROSE) cells. We determined that constitutive activation of the Raf, phosphatidylinositol 3-kinase, or Ral guanine nucleotide exchange factor effector pathway alone was not sufficient to down-regulate Par-4 in RIE-1 or ROSE cells. However, treatment of Ras-transformed RIE-1 or ROSE cells with the MEK inhibitors U0126 and PD98059 increased Par-4 protein expression. Thus, although oncogenic Ras utilizes the Raf/MEK/ERK pathway to down-regulate Par-4 in both fibroblasts and epithelial cells, Ras activation of an additional signaling pathway(s) is required to achieve the same outcome in epithelial cells. Methylation-specific PCR showed that the par-4 promoter is methylated in Ras-transformed cells through a MEK-dependent pathway and that treatment with the DNA methyltransferase inhibitor azadeoxycytidine restored Par-4 mRNA transcript and protein levels, suggesting that the mechanism for Ras-mediated down-regulation of Par-4 is by promoter methylation. Support for this possibility is provided by our observation that Ras transformation was associated with up-regulation of Dnmt1 and Dnmt3 DNA methyltransferase expression. Finally, ectopic Par-4 expression significantly reduced Ras-mediated growth in soft agar, but not morphological transformation, highlighting the importance of Par-4 down-regulation in specific aspects of Ras-mediated transformation of epithelial cells.

Overexpression of Collagenase 1 (MMP-1) Is Mediated by the ERK Pathway in Invasive Melanoma Cells

Melanoma progresses as a multistep process where the thickness of the lesion and depth of tumor invasion are the best prognostic indicators of clinical outcome. Degradation of the interstitial collagens in the extracellular matrix is an integral component of tumor invasion and metastasis, and much of this degradation is mediated by collagenase-1 (MMP-1), a member of the matrix metalloproteinase (MMP) family. MMP-1 levels increase during melanoma progression where they are associated with shorter disease-free survival. The Ras/Raf/MEK/ERK mitogen-activated protein kinase (MAPK) pathway is a major regulator of melanoma cell proliferation. Recently, BRAF has been identified as a common site of activating mutations, and, although many reports focus on its growth-promoting effects, this pathway has also been implicated in progression toward metastatic disease. In this study, we describe four melanoma cell lines that produce high levels of MMP-1 constitutively. In each cell line the Ras/Raf/MEK/ERK pathway is constitutively active and is the dominant pathway driving the production of MMP-1. Activation of this pathway arises due to either an activating mutation in BRAF (three cell lines) or autocrine fibroblast growth factor signaling (one cell line). Furthermore, blocking MEK/ERK activity inhibits melanoma cell proliferation and abrogates collagen degradation, thus decreasing their metastatic potential. Importantly, this inhibition of invasive behavior can occur in the absence of any detectable changes in cell proliferation and survival. Thus, constitutive activation of this MAPK pathway not only promotes the increased proliferation of melanoma cells but is also important for the acquisition of an invasive phenotype.

Opposing roles of the extracellular signal-regulated kinase and p38 mitogen-activated protein kinase cascades in Ras-mediated downregulation of tropomyosin

We showed previously that activated Ras, but not Raf, causes transformation of RIE-1 epithelial cells, demonstrating the importance of Raf-independent pathways in mediating Ras transformation. To assess the mechanism by which Raf-independent effector signaling pathways contribute to Ras-mediated transformation, we recently utilized representational difference analysis to identify genes expressed in a deregulated fashion by activated Ras but not Raf. One gene identified in these analyses encodes for alpha-tropomyosin. Therefore, we evaluated the mechanism by which Ras causes the downregulation of tropomyosin expression. By using RIE-1 cells that harbor inducible expression of activated H-Ras(12V), we determined that the downregulation of tropomyosin expression correlated with the onset of morphological transformation. We found that the reversal of Ras transformation caused by inhibition of extracellular signal-regulated kinase activation corresponded to a restoration of tropomyosin expression. Inhibition of p38 activity in Raf-expressing RIE-1 cells caused both morphological transformation and loss of tropomyosin expression. Thus, a reduction in tropomyosin expression correlated strictly with morphological transformation of RIE-1 cells. However, forced overexpression of tropomyosin in Ras-transformed cells did not reverse morphological or growth transformation, a finding consistent with the possibility that multiple changes in gene expression contribute to Ras transformation. We also determined that tropomyosin expression was low in two human tumor cell lines, DLD-1 and HT1080, that harbor endogenous mutated alleles of ras, but high in transformation-impaired, derivative cell lines in which the mutant ras allele has been genetically deleted. Finally, treatment with azadeoxycytidine restored tropomyosin expression in Ras-transformed RIE-1, HT1080, and DLD-1 cells, suggesting a role for DNA methylation in downregulating tropomyosin expression.

Loss of transgelin in breast and colon tumors and in RIE-1 cells by Ras deregulation of gene expression through Raf-independent pathways

Activated Ras but not Raf can transform RIE-1 and other epithelial cells, indicating the critical importance of Raf-independent effector function in Ras transformation of epithelial cells. To elucidate the nature of these Raf-independent activities, we utilized representational difference analysis to identify genes aberrantly expressed by Ras through Raf-independent mechanisms in RIE-1 cells. We identified a total of 22 genes, both known and novel, whose expression was either activated or abolished by Ras but not Raf. The genes up-regulated encode proteins involved in protein or DNA synthesis, regulation of protease activity, or ligand binding, whereas those genes down-regulated encode actin cytoskeletal-, extracellular matrix-, and gap junction-associated proteins, and transmembrane receptor- or cytokine-like proteins. These results suggest that a key function of Raf-independent signaling involves deregulation of gene expression. We further characterized transgelin as a gene whose expression was abolished by Ras. Transgelin was identified previously as a protein whose expression was lost in virally transformed cell lines. We show that this loss is regulated at the level of gene expression and that both Raf-dependent and Raf-independent pathways are required to cause Ras down-regulation of transgelin in RIE-1 cells, whereas Raf alone is sufficient to cause its loss in NIH 3T3 fibroblasts. We also found that Ras-dependent and Ras-independent mechanisms can cause the down-regulation of transgelin in human breast and colon carcinoma cells lines and patient-derived tumor samples. We conclude that loss of transgelin gene expression may be an important early event in tumor progression and a diagnostic marker for breast and colon cancer development.

Identification of Ras-regulated genes by representational difference analysis

In conclusion, RDA provides a fast, technically simple, and inexpensive way to characterize genes aberrantly expressed due to Ras transformation. The identification and characterization of these genes may provide insight not only into the mechanism by which Ras causes transformation, but also may identify novel targets for rational drug design and development of anticancer drugs.

The gut-enriched Kruppel-like factor (Kruppel-like factor 4) mediates the transactivating effect of p53 on the p21WAF1/Cip1 promoter

An important mechanism by which the tumor suppressor p53 maintains genomic stability is to induce cell cycle arrest through activation of the cyclin-dependent kinase inhibitor p21(WAF1/Cip1) gene. We show that the gene encoding the gut-enriched Krüppel-like factor (GKLF, KLF4) is concurrently induced with p21(WAF1/Cip1) during serum deprivation and DNA damage elicited by methyl methanesulfonate. The increases in expression of both Gklf and p21(WAF1/Cip1) due to DNA damage are dependent on p53. Moreover, during the first 30 min of methyl methanesulfonate treatment, the rise in Gklf mRNA level precedes that in p21(WAF1/Cip1), suggesting that GKLF may be involved in the induction of p21(WAF1/Cip1). Indeed, GKLF activates p21(WAF1/Cip1) through a specific Sp1-like cis-element in the p21(WAF1/Cip1) proximal promoter. The same element is also required by p53 to activate the p21(WAF1/Cip1) promoter, although p53 does not bind to it. Potential mechanisms by which p53 activates the p21(WAF1/Cip1) promoter include a physical interaction between p53 and GKLF and the transcriptional induction of Gklf by p53. Consequently, the two transactivators cause a synergistic induction of the p21(WAF1/Cip1) promoter activity. The physiological relevance of GKLF in mediating p53-dependent induction of p21(WAF1/Cip1) is demonstrated by the ability of antisense Gklf oligonucleotides to block the production of p21(WAF1/Cip1) in response to p53 activation. These findings suggest that GKLF is an essential mediator of p53 in the transcriptional induction of p21(WAF1/Cip1) and may be part of a novel pathway by which cellular responses to stress are modulated.

Understanding Ras: 'it ain't over 'til it's over'

Since 1982, Ras has been the subject of intense research scrutiny, focused on determining the role of aberrant Ras function in human cancers and defining the mechanism by which Ras mediates its actions in normal and neoplastic cells. The long-term goal has been to develop antagonists of Ras as novel approaches for cancer treatment. Although impressive strides have been made in these endeavours, and our knowledge of Ras is quite extensive, it appears that we are at the beginning, rather than at the end, of fully understanding Ras function. This review highlights new issues that have further complicated our efforts to understand Ras.

The gut-enriched Krüppel-like factor suppresses the activity of the CYP1A1 promoter in an Sp1-dependent fashion

The gut-enriched Krüppel-like factor (GKLF) is a newly identified zinc finger-containing transcription factor. Recent studies indicate that GKLF binds to a core DNA sequence of 5'-(G/A)(G/A)GG(C/T)G(C/T)-3', which is found in an endogenous cis element, the basic transcription element (BTE) of the cytochrome P-450IA1 (CYP1A1) promoter. The present study characterizes the ability of GKLF to regulate CYP1A1 expression. By electrophoretic mobility gel shift assay (EMSA) and methylation interference assay, GKLF was found to bind BTE in a manner similar to several other transcription factors known to interact with BTE including Sp1 and BTEB. Cotransfection studies in Chinese hamster ovary cells showed that GKLF inhibited the CYP1A1 promoter in a dose- and BTE-dependent manner. The same experiments also revealed that BTE was responsible for a significant portion of the CYP1A1 promoter activity. EMSA of nuclear extracts from Chinese hamster ovary cells showed that Sp1 and Sp3 were two major proteins that interacted with BTE. Additional cotransfection studies showed that GKLF inhibited Sp1-mediated activation of the CYP1A1 promoter. In contrast, GKLF enhanced Sp3-dependent suppression of the same promoter. Moreover, the ability of GKLF to inhibit Sp1-dependent transactivation was in part due to physical interaction of the two proteins. These findings indicate that GKLF is a negative regulator of the CYP1A1 promoter in a BTE-dependent fashion and that this inhibitory effect is in part mediated by physical interaction with Sp1.

Size-dependent increase in prostanoid levels in adenomas of patients with familial adenomatous polyposis

Recent studies indicate that nonsteroidal anti-inflammatory drugs have a chemopreventive effect against colorectal neoplasia. Nonsteroidal anti-inflammatory drugs inhibit cyclooxygenases, principal enzymes that mediate the formation of prostanoids. To determine whether prostanoids are involved in the pathogenesis of colorectal adenomas, we compared the levels of five major stable metabolic products of the cyclooxygenase pathway in the normal-appearing mucosa and in adenomas of patients with familial adenomatosis polyposis. Of 12 patients tested, 6 had elevated levels of at least one prostanoid in the adenomas. More importantly, the relative levels of three prostanoids [prostaglandin (PG)D2, PGE2, and 6-keto-PGF1alpha] were elevated in adenomas compared to normal-appearing mucosa from the same patients, and the resulting ratios were correlated with the size of the adenoma. These results suggest a role for prostanoids in progression of colorectal polyposis in familial adenomatosis polyposis patients.

Identification of the DNA sequence that interacts with the gut-enriched Krüppel-like factor

The gut-enriched Krüppel-like factor (GKLF) is a recently identified eukaryotic transcription factor that contains three C2H2zinc fingers. The amino acid sequence of the zinc finger portion of GKLF is closely related to several Krüppel proteins, including the lung Krüppel-like factor (LKLF), the erythroid Krüppel-like factor (EKLF) and the basic transcription element binding protein 2 (BTEB2). The DNA sequence to which GKLF binds has not been definitively established. In the present study we determined the DNA binding sequence of GKLF using highly purified recombinant GKLF in a target detection assay of an oligonucleotide library consisting of random sequences. Upon repeated rounds of selection and subsequent characterization of the selected sequences by base-specific mutagenesis a DNA with the sequence 5'-G/AG/AGGC/TGC/T-3' was found to contain the minimal essential binding site for GKLF. This sequence is present in the promoters of two previously characterized genes: the CACCC element of the beta-globin gene, which interacts with EKLF, and the basic transcription element (BTE) of the CYP1A1 gene, which interacts with Sp1 and several Sp1-like transcription factors. Moreover, the selected GKLF binding sequence was capable of mediating transactivation of a linked reporter gene by GKLF in co-transfection experiments. Our results establish GKLF as a sequence-specific transcription factor likely involved in regulation of expression of endogenous genes.

Expression of the gut-enriched Krüppel-like factor gene during development and intestinal tumorigenesis

We examined the expression of GKLF (gut-enriched Krüppel-like factor), a recently identified zinc finger-containing transcription factor, in mice during development using the ribonuclease protection assay. In the adult, the level of GKLF transcript is abundant throughout the gastrointestinal tract. Between embryonic days 10 and 19 (E10 and E19) of development, the initial level of whole embryo GKLF transcript is low but begins to rise on E13 and peaks on E17. In the newborn, GKLF transcript level is higher in the colon than in the small intestine although the levels in both organs rise with increasing age. Expression of GKLF was also examined in the intestinal tract of the Min mouse, a model of intestinal tumorigenesis. The level of GKLF transcript is significantly decreased in the intestine of Min mice during a period of tumor formation when compared to age-matched control littermates. Our findings indicate that GKLF expression correlates with certain periods of gut development and is down-regulated during intestinal tumorigenesis, suggesting that GKLF may play a role in gut development and/or tumor formation.

Two potent nuclear localization signals in the gut-enriched Krüppel-like factor define a subfamily of closely related Krüppel proteins

The gut-enriched Krüppel-like factor (GKLF) is a newly identified transcription factor that contains three C2H2 Krüppel-type zinc fingers. Previous immunocytochemical studies indicate that GKLF is exclusively localized to the nucleus. To identify the nuclear localization signal (NLS) within GKLF, cDNA constructs with various deletions in the coding region of GKLF were generated and analyzed by indirect immunofluorescence in transfected COS-1 cells. In addition, constructs fusing regions representing putative NLSs of GKLF to green fluorescent protein (GFP) were generated and examined by fluorescence microscopy in similarly transfected cells. The results indicate that GKLF contains two potent, independent NLSs: one within the zinc fingers and the other in a cluster of basic amino acids (called 5' basic region) immediately preceding the first zinc finger. In comparison, putative NLSs within the zinc fingers and the 5' basic region of a related Krüppel protein, zif268/Egr-1, are relatively less efficient in their ability to translocate GFP into the nucleus. A search in the protein sequence data base revealed that despite the existence of numerous Krüppel proteins, only two, the lung Krüppel-like factor (LKLF) and the erythroid Krüppel-like factor (EKLF), exhibit similar NLSs to those of GKLF. These findings indicate that GKLF, LKLF, and EKLF are members of a subfamily of closely related Krüppel proteins.

Colonic epithelium-enriched protein A4 is a proteolipid that exhibits ion channel characteristics

Expression of the human gene A4 is enriched in the colonic epithelium and is transcriptionally activated on differentiation of colonic epithelial cells in vitro (M. M. Oliva, T. C. Wu, and V. W. Yang. Arch. Biochem. Biophys. 302: 183-192, 1993). A4 cDNA contains an open reading frame that predicts a polypeptide of 17 kDa. To determine the function of the A4 protein, we characterized its biochemical and physiological properties. Hydropathy analysis of deduced A4 amino acid sequence revealed four putative membrane-spanning alpha-helices. The hydrophobic nature of A4 was confirmed by its being extractable with organic solvents. Immunocytochemical studies of cells expressing A4 localized it to the endoplasmic reticulum. Moreover, A4 multimerized in vivo as determined by coimmunoprecipitation experiments. The four-transmembrane topology and biophysical characteristics of A4 suggest that it belongs to a family of integral membrane proteins called proteolipids, some of which multimerize to form ion channels. Subsequent electrophysiological studies of nuclei isolated from microinjected Xenopus laevis oocytes transiently expressing A4 showed the appearance of a 28-pS channel. Thus our studies indicate that A4 is a colonic epithelium-enriched protein localized to the endoplasmic reticulum and that, similar to other proteolipids, A4 multimerizes and exhibits characteristics of an ion channel.

Identification and characterization of a gene encoding a gut-enriched Krüppel-like factor expressed during growth arrest

A cDNA clone, named gut-enriched Krüppel-like factor (GKLF), was isolated from an NIH 3T3 library using a probe encoding the zinc finger region of the immediate-early transcription factor zif/268. The deduced GKLF amino acid sequence contains three tandem zinc fingers that are related to members of the Krüppel family of transcription factors. By indirect immunofluorescence, GKLF is localized to the cell nucleus. In cultured fibroblasts, GKLF mRNA is found in high levels in growth-arrested cells and is nearly undetectable in cells that are in the exponential phase of proliferation. The growth-arresting nature of GKLF is demonstrated by an inhibition of DNA synthesis in cells transfected with a GKLF-expressing plasmid construct. In the mouse, GKLF mRNA is present in select tissues and is most abundant in the colon, followed by the testis, lung, and small intestine. In situ hybridization experiments indicate that GKLF mRNA is enriched in epithelial cells located in the middle to upper crypt region of the colonic mucosa. Taken together, these results suggest that GKLF is potentially a negative regulator of cell growth in tissues such as the gut mucosa, where cell proliferation is intimately coupled to growth arrest and differentiation.

Galactose consumption, metabolism, and follicle-stimulating hormone concentrations in women of late reproductive age

OBJECTIVE

To test the hypothesis that high galactose consumption and low activity of galactose-1-phosphate uridyl transferase (transferase) is associated with early ovarian senescence among nongalactosemic women.

DESIGN

Cross-sectional study. Data collection consisted of a self-administered questionnaire with sections on diet (food frequency data to measure galactose consumption), reproductive, and medical histories. One blood sample was collected to measure FSH and transferase activity; FSH was used as a measure of ovarian senescence. Among women who were having menstrual periods at least every 8 weeks, the blood sample was drawn in the early follicular phase (days 2 to 4) of a menstrual cycle.

PARTICIPANTS

Two hundred ninety-five women volunteers ages 38 to 49 years who had not had a hysterectomy or oophorectomy were recruited through posters and advertisements.

MAIN OUTCOME MEASURE

Serum FSH concentrations.

RESULTS

Controlling for age, smoking, and body mass, transferase activity and FSH were unrelated. However, FSH levels were 29% higher (95% confidence intervals, 9% to 52%) among women who reported consuming > or = 6 g galactose/d.

CONCLUSION

These data do not support the hypothesis that low transferase activity represents a genetic predisposition for early ovarian senescence, as measured by FSH levels in women ages 38 to 49 years. However, the hypothesized positive association between galactose consumption and FSH was supported.

High-resolution immunogold localization of Giardia cyst wall antigens using field emission SEM with secondary and backscatter electron imaging

We describe here the ultrastructural localization of Giardia cyst antigens in the filaments associated with the outer portion of intact cysts and on developing cyst wall filaments in encysting trophozoites. Post-embedding immunogold labeling of thin sections of intact Giardia cysts with polyclonal and monoclonal antibodies specific for cyst wall antigens (major protein bands of approximately 29, 75, 88, and 102 KD on Western blots) showed strong labeling of the filamentous cyst wall, whereas no labeling was seen on the membranous portion. High-resolution field emission scanning electron microscopy (FESEM) of Giardia cysts revealed that the cyst wall-specific polyclonal rabbit antisera and monoclonal mouse antibody produced gold labeling of 20-nm filaments in the cyst wall as detected with secondary electron imaging (SEI) and backscatter electron imaging (BEI) at 10 kV, despite coating of the cells with platinum by ion sputtering. FESEM studies of encysting Giardia trophozoites demonstrated that immunostaining with antibodies to cyst wall antigens produced colloidal gold labeling of developing cyst wall filaments on the cell surface; however, the intervening membrane domains were unlabeled. Substitution of normal serum for cyst wall-specific antibodies, or preabsorption of specific antibodies with Giardia cysts, eliminated immunolabeling of the filaments.

Signal transduction in human neutrophil leucocytes: effects of external Na+ and Ca2+ on cell polarity

Stimulation of neutrophil leucocytes with chemotactic factors is known to result in membrane permeability changes, as evidenced by fluxes of Na+ and K+ across the cell membrane together with an increased uptake of Ca2+ from the medium. These fluxes have been implicated in the transduction mechanisms of various responses, including locomotion and subsequent chemotaxis. We have previously reported that exposure of unstimulated, round neutrophils held in suspension, to the chemotactic peptide fMet-Leu-Phe confers morphological polarity on the neutrophils by stimulating waves of contraction, which are also intimately connected with locomotion on an appropriate substratum. As the acquisition of polarity is the important first step in the chemotactic response we have investigated the effects of modifying the external ionic environment and of various ion channel blockers on the polarizing response of neutrophils held in suspension. Removal and chelation of both Ca2+ and Mg2+ from the external medium did not inhibit the acquisition of polarity and a variety of inorganic Ca2+ channel blockers together with the organic Ca2+ antagonists, verapamil and D600, were ineffective in inhibiting the response. Replacement of Na+ in the external medium with choline inhibited the polarizing response completely but tetrodotoxin, which blocks fast Na+ channels, and amiloride, which inhibits Na+/K+ exchange, had no effect. Inhibition of the Na+/K+-ATPase with ouabain and also tetraethylammonium ions, which block potassium channels, had no inhibiting effect on polarization. These results indicate that while Ca2+ and Mg2+ are not required in the external medium, Na+ is essential, and therefore Na+/K+ fluxes across the cell membrane play a role in initiating locomotion.

An alternative health care setting for children with cancer: a residential summer camp

Increasing concern for the psychosocial needs of children with cancer has paralleled increasing survival rates. This paper discusses the way in which a summer camp program can help to meet many social needs of children with cancer. Also discussed is the proposal of a campsite to be operated year-round for families of children with cancer, and the way in which such a program can help to meet many needs of these families.

Neutrophil leucocyte chemotaxis: a simplified assay for measuring polarizing responses to chemotactic factors

A method is described which greatly simplifies the screening of compounds which are potentially chemotactic for neutrophil leucocytes. Neutrophils isolated from blood by a standardised procedure are greater than 95% spherical in morphology. Addition of chemotactic factors in isotropic, non-gradient, concentrations induces the spherical shape to become polarized. The degree of polarity depends on the concentration of the factor used, as does the percentage of cells which become polarised. All compounds which induce a good response in assays measuring cell accumulation or orientation in gradients induced a consistent polarizing response in non-gradient conditions with the cells held in suspension. The advantage of this simplified assay over methods currently in use are discussed.

Behaviour of neutrophil leucocytes in uniform concentrations of chemotactic factors: contraction waves, cell polarity and persistence

The essential component of any hypothesis of random or directed cell movement is the mechanism of cell polarity. In this paper we describe the polar behaviour of human neutrophil leucocytes in uniform concentrations of chemotactic factors both in suspension and while moving across surfaces. Neutrophils exposed to uniform concentrations of chemotactic factors in suspension around the dissociation constant (Kd) for the receptor rapidly become distinctly bipolar; neutrophils exposed to supraoptimal uniform concentrations (100-fold greater than Kd) of chemotactic factors in suspension, although morphologically active, never reached the same degree of polarity as cells in optimal concentrations. These differences in polarity were shown to be the direct result of equatorial contraction waves stimulated on the cell surface by interaction with chemotactic factors. In optimal concentrations of chemotactic factors, contraction waves were initiated from one region of the cell, whereas in supraoptimal concentrations of chemotactic factors contraction waves emanated from all areas of the cell surface. Asymmetry in the distribution of surface receptors for Fc and C3b were observed in neutrophils polarized in uniform concentrations of chemotactic factor. In neutrophils, motile but not well polarized (in 10(−6) M-N-formylmethionyl-leucyl-phenylalanine (fMLP), receptors were uniformly distributed. In neutrophils polarized in concentrations of fMLP near the Kd for the receptor (10(−8) M) receptors for C3b and Fc were localized in the anterior region of the moving cell. The link between contraction waves, cell polarity and receptor redistribution and their initiation by chemotactic peptides is discussed in the context of neutrophil locomotion and response to chemical signals.

Contraction waves in lymphocyte locomotion

In this paper we propose that the constriction ring, a prominent feature of moving leucocytes, is a major source of locomotive force. Analysis of time-lapse films of lymphocytes in suspension and moving through three-dimensional collagen gels, demonstrated that the constriction ring was the morphological manifestation of a wave of circular contraction that moved antero-posteriorly. In lymphocytes in suspension the wave moved, although the cells could not. Analysis of lymphocytes moving through a collagen gel revealed that the waves remained stationary with respect to the external environment while the cell appeared to move forward through them. Passage of a single equatorial contraction wave resulted in cell lengthening: a shortening of the region posterior to the constriction was observed in cells moving through collagen gels, but not in lymphocytes held in suspension, suggesting that attachment of cells to the collagen network was necessary for longitudinal contraction. Lymphocyte attachment to collagen gels was mediated through the rapid extension of bleb-like structures into the collagen network. Transmission electron microscopy (TEM) failed to demonstrate any organized structure at the constriction ring. NBD-Phallacidin staining of lymphocytes together with TEM demonstrated that F-actin was distributed evenly throughout the length of the cell. Cell polarity was clearly recognizable by the distribution of coated vesicles, microvilli, and all organelles to the rear, and Thy 1–2 to the front, of motile cells, but polarity could be reversed by the passage of a single contraction wave starting at the rear of the cell, without prior redistribution of these structures.

Invasion of collagen gels by mouse lymphoid cells

Small mouse lymphocytes from lymph nodes rapidly invaded three-dimensional collagen gels (in the absence of any added chemical attractant). In short-term assays (2-8 hr) this property was restricted to 20-25% of the cell population. Invasion was an active process involving cell locomotion. Time-lapse cinematography revealed that movement was erratic with frequent changes in cell speed. Tracks of cell paths within collagen gels demonstrated that lymphocytes made narrow angles of turn and thus showed a 'persistent random-walk' similar to other cell types moving on plane substrata. Analysis of lymphocyte movement within aligned collagen gels demonstrated that locomotion was biased in the axis of fibre alignment, i.e. lymphocytes showed contact guidance. Separated B lymphocytes invaded collagen gels at a slower rate than unseparated lymph node cells, as also did T cells purified by filtration through nylon wool columns. This latter anomaly implied that nylon wool filtration selectively depleted cells with invasive characteristics from a heterogeneous lymphocyte population. A comparison of Peyer's patch and lymph node lymphocytes showed that both populations invaded at the same rate but the latter cell type did this in greater numbers. This difference may reflect the different proportions of B and T lymphocytes in the two tissues. Lymphocytes from oxazolone-stimulated lymph nodes showed greatly increased movement into collagen matrices compared to unstimulated control lymph node lymphocytes. This increase was demonstrated to be a property of the blast cell population by separating the cells on Percoll gradients into lymphoblast-enriched and -depleted populations.

The orientation of fibroblasts and neutrophils on elastic substrata

The reaction of fibroblasts to the elastic properties of the substratum was studied using elastic collagen films. These films were stretched in one axis to give a substratum which was anisotropic in its elasticity and deformability. Analysis of the orientation of fibroblasts cultured on these substrata showed that they oriented along the axis of stretch which was also the axis of fibre alignment. This orientation was significantly reduced when the films were made less elastic by attachment to a glass slide and chemical fixation. Neither of these procedures appeared to alter the surface shape of these films, which suggests that the elastic properties of the substratum markedly influence the orientation of fibroblasts. The orientation of locomotion of neutrophil leukocytes on elastic collagen films was also analysed and no bias along the axis of stretch was observed. This was compared with neutrophil locomotion in 3-D stretched collagen gels, in which a strong bias along the axis of stretch and of fibre alignment was observed. The possible reasons for the response of these two cell types is discussed.

Separation of mouse lymphoblasts by discontinuous density centrifugation on Percoll gradients

Mouse lymphoblasts generated in vivo by a topical application of the contact sensitizer oxazolone or by the contents of the gut lumen were separated by discontinuous density centrifugation on Percoll gradients. A 3-step gradient was used to divide the cells into two subpopulations. For cells from oxazolone stimulated lymph nodes, the low density band contained 20-30% of the initial cell number applied to the gradient; 25-40% of this population were in S phase and nearly all the large and pyroninophilic cells were confined to this layer. The high density step cells (70-80% of initial cell number) were predominantly small lymphocytes with less than 0.5% in S phase. Similar results were obtained using cells from picryl chloride stimulated lymph nodes or from mesenteric lymph nodes.

Some determinants of the locomotory behaviour of phagocytes and lymphocytes in vitro

In this review, we discuss some physical and chemical determinants of locomotor behaviour of phagocytic cells and lymphocytes as studied in visual assays, paying particular attention to the following points. (a) A distinction is made between chemokinesis and other forms of kinesis. We propose that the term chemokinesis be reserved for responses resulting from selective recognition of chemical substances. Many kineses in leucocytes may not involve such recognition, but may result from a variety of physical factors, such as those that alter the adhesiveness between cell and substratum. (b) Neutrophils moving in aligned gels of collagen or fibrin show contact guidance of locomotion, i.e. bidirectional movement along the axis of alignment of the fibres of the gel. Thus neutrophils show directional locomotion not only in chemotactic gradients but also in response to physical properties of the substratum. (c) Lymphocytes adhere poorly and move poorly on 2D protein coated substrata. However they move rapidly through 3D collagen gels. This locomotion may be independent of adhesion since lymphocytes may gain traction for locomotion by expanding pseudopods into gaps in the gel matrix, then using the pseudopod as an anchor for subsequent locomotion in any direction.

Lymphocyte locomotion and attachment on two-dimensional surfaces and in three-dimensional matrices

The adhesion and locomotion of mouse peripheral lymph node lymphocytes on 2-D protein- coated substrata and in 3-D matrices were compared. Lymphocytes did not adhere to, or migrate on, 2-D substrata suck as serum- or fibronectin-coated glass. They did attach to and migrate in hydrated 3-D collagen lattices. When the collagen was dehydrated to form a 2-D surface, lymphocyte attachment to it was reduced. We propose that lymphocytes, which are poorly adhesive, are able to attach to and migrate in 3-D matrices by a nonadhesive mechanism such as the extension and expansion of pseudopodia through gaps in the matrix, which could provide purchase for movement in the absence of discrete intermolecular adhesions. This was supported by studies using serum-coated micropore filters, since lymphocytes attached to and migrated into filters with pore sizes large enough (3 or 8 mum) to allow pseudopod penetration but did not attach to filters made of an identical material (cellulose esters) but of narrow pore size (0.22 or 0.45 mum). Cinematographic studies of lymphocyte locomotion in collagen gels were also consistent with the above hypothesis, since lymphocytes showed a more variable morphology than is typically seen on plane surfaces, with formation of many small pseudopodia expanded to give a marked constriction between the cell and the pseudopod. These extensions often remained fixed with respect to the environment as the lymphocyte moved away from or past them. This suggests that the pseudopodia were inserted into gaps in the gel matrix and acted as anchorage points for locomotion.

Relations between Fc receptor function and locomotion in human lymphocytes

The relationship between the surface binding sites on human lymphocytes for chemotactic factors and for the Fc fraction of IgG was investigated using both blood lymphocytes and established cultures of human lymphoblasts. Pretreatment of human blood lymphocytes with a variety of chemotactic factors inhibited Fc-rosette formation. This was true even of small formylated peptides, for example, formyl-methionyl-phenylalanine (chemotactic) inhibited Fc-rosetting but unformylated methionyl-phenylalanine (non-chemotactic) did not. Conversely pretreatment of lymphocytes with IgG inhibited their locomotor reactions to a variety of chemoattractants. Aggregated IgG was more inhibitory than non-aggregated IgG and the inhibition was mediated via the Fc piece. In a filter assay, native IgG was chemokinetic but not chemotactic for lymphocytes. Heat-aggregated IgG induced more locomotion of lymphocytes than native IgG, and was possibly chemotactic, but no unequivocally so. The possibility that chemotactic factors and the Fc portion of IgG compete for the same cell surface receptor was investigated by binding studies using cultured lymphoblasts. These studies suggested that the reciprocal inhibition could not be explained by competition for receptors. An alternative explanation was suggested by the finding that inhibition of locomotion by aggregated IgG was dependent on the presence of divalent cations at the time the IgG was added, and did not occur in the presence of the calcium ionophore A23187. Addition of aggregated IgG or chemotactic factors to lymphocytes thus may lead to a gated entry of calcium, and following closure of the calcium gate, the cells become relatively unresponsive to further stimulation.

Using pantographic tracings to detect TMJ and muscle dysfunctions

Forty-six subjects were examined using the HDI and a PRI. Two sets of pantographic tracings were used to determine if subjects experiencing dysfunction could differentiate between degrees of dysfunction. Subjects were divided into groups according to their clinical symptoms: none (D0), sligh (D1), and moderate dysfunction (D5). Each subject was further classified into one of two groups according to his state of occlusion/articulation. The PRI detected differences between the group with moderate dysfunction and those groups with no dysfunction and slight dysfunction on the basis of differences between the first and second sets of tracings; no difference was found between the groups with slight and moderate dysfunction. Subjects with poor occlusions had higher PRI scores. The diagnosis of TMJ dysfunction may require the use of several modalities such as subjective responses, clinical examination, radiographs, and pantographic tracings.