The Ron oncogenic activity induced by the MEN2B-like substitution overcomes the requirement for the multifunctional docking site

Oncogenic activation of the Ron tyrosine kinase (Macrophage Stimulating Protein receptor) relies on substitutions of two highly conserved residues in the catalytic domain (D1232V and M1254T), which result in ligand-independent activation of the receptor, in vivo tumorigenesis and metastasis. We show here that the Y/F conversion of the Y1317 residue in the kinase domain impairs tumorigenic and metastatic properties of Ron activated by the MEN2B-like mutation (RonM1254T), but not by other two oncogenic substitutions. Furthermore, RonM1254T lacking the multifunctional docking site retains transforming and metastatic activity. These data reveal that the transforming activity of RonM1254T mutant is dependent on Y1317 phosphorylation, suggesting a shift in intramolecular substrate specificity. Consistently, a shift of RonM1254T kinase substrate specificity was observed by in vitro peptide phosphorylation assays and in vivo receptor auto-phosphorylation. The Y1317 phosphorylation elicits by itself activation of PI-3K/Akt and MAPK signalling pathways. Our data indicate that the accomplishment of the full oncogenic phenotype of RonM1254T requires the phosphorylation both of the canonical C-terminal docking site and of the unique Y1317 residue in the tyrosine kinase domain.

Gene transfer of a secretable form of IL-15 in murine adenocarcinoma cells: effects on tumorigenicity, metastatic potential and immune response

IL-15 is an immunostimulatory cytokine with IL-2-like activities. To exploit the potential role of IL-15 in cancer immuno-/gene therapy, we engineered murine TS/A cells with different IL-15 cDNA constructs. Significant IL-15 secretion was achieved only by the use of a modified cDNA encoding for an IL-15 pre-protein bearing the IgK light chain signal peptide. Different TS/A clones (TS/A IL-15 C6, C23, C29) producing 390 to 1,600 pg/ml biologically active IL-15 showed reduced tumorigenicity when implanted s.c. in syngeneic mice and significantly reduced metastatic potential by i.v. injection. Tumorigenicity of s.c. TS/A IL-15 was restored in animals depleted of CD8(+) lymphocytes or of natural killer cells and partially in CD4(+)-depleted mice. TS/A IL-15 cells displayed a significantly reduced growth rate by s.c. implant in nude mice. Also, >50% syngeneic animals rejecting TS/A IL-15 were resistant to a subsequent rechallenge with wild-type tumor (TS/Apc), indicating induction of protective immunity against TS/A tumor-associated antigens (TAAs). Cytolytic T lymphocyte (CTL) activity, specifically inhibited by anti-CD3 antibodies, was inducible in the splenocytes of TS/A IL-15-immunized animals by mixed lymphocyte/tumor culture (MLTC), and IFN-gamma was released in the supernatant of MLTC, mainly by CD8(+) cells. Immunohistochemistry of the TS/A IL-15 tumor area revealed the presence of an inflammatory infiltrate with predominant natural killer, macrophage, and granulocyte components and expression of IFN-gamma as a distinctive secondary cytokine. Use of TS/A IL-15 mitomycin-treated cells for therapeutic vaccination in experimental TS/A metastasis was effective in 60% of animals treated; these animals showed no metastatic tumor growth.

Anorectal malformations associated with enteric dysganglionosis in Danforth's short tail (Sd) mice

BACKGROUND

The spontaneous mutant Danforth's short tail (Sd) mouse has been studied over the last 60 years from the morphological, embryological, and genetic point of view. The Sd mutation affects a gene essential to notochordal development, and the Sd mouse phenotype represents an analogue of human caudal regression syndrome. The Sd/Sd mouse presents different types of anorectal malformations (ARM) and was suggested as a simple and cheap model of investigation of ARM morphology and embryology. In the current study, the Sd mouse enteric nervous system (ENS) was thoroughly investigated with specific immunohistochemical markers.

METHODS

Macroscopic analysis, normal histology, and immunohistochemical techniques for detecting neurofilaments (NF) and NOS1 were used to study ENS of 138 Sd mice and 25 controls.

RESULTS

The surprising results of this study showed that Sd mutation is associated with different degrees of hypoganglionosis and aganglionosis. In 41% of Sd/SD-affected mice, the rectal pouch was aganglionic and in the remaining 58% was severely hypoganglionic. In addition, 4.1% of heterozygous mice presented a distal aganglionosis and 8.3% hypoganglionosis.

CONCLUSIONS

These results suggest that Sd mutation independently affects distinct cell lines during early organogenesis, as notochord cells, ventral hingut endoderm, and neuroblasts migrating from neural crest cells. Comparing the Sd murine model with human pathology, this study confirms that the association between ARM and intestinal dysganglionosis is not rare and underlines the importance of detecting in every ARM patient the innervation abnormalities of rectal pouch and fistulas.

Anxiety, depression, hunger and body composition: III. Their relationships in obese patients

The present paper explores the relationships between anxiety, depression, hunger sensation and body composition in obese patients (OP). The aim is to detect whether or not there are abnormalities in these relationships in OP as compared to clinically healthy subjects (CHS). The study was performed on 22 CHS (2 M, 20 W; mean age = 24 +/- 2 years; mean body mass index = 21 +/- 2 kg/m2) and 48 OP (4 M, 44 W; mean age = 40 +/- 17 years; mean body mass index = 32 +/- 7 kg/m2). Anxiety and depression were found to be correlated, negatively, with the relative lean body mass, and, positively, with the fat body mass in OP but not in CHS. These findings corroborate the idea that anxiety and depression can reach an abnormal expression when obesity shows its worst loss in lean body mass and its highest expansion in adipocyte mass. As hunger sensation was found not to correlate with either anxiety or depression in OP, the opinion is expressed that the impairment of anxio-depressive integrity is a corollary of obesity rather than a primary affective disorder leading to obesity via an enhanced food intake.

DNA vaccination against the ovarian carcinoma-associated antigen folate receptor alpha (FRalpha) induces cytotoxic T lymphocyte and antibody responses in mice

Human folate receptor alpha (FRalpha) is a folate-binding protein that is selectively overexpressed in ovarian carcinoma and has been regarded as a suitable target antigen for immunotherapy purposes. To study the possible use of this antigen in DNA vaccination, FRalpha cDNA was ligated into the VR1012 (Vical) expression vector under the transcriptional control of the cytomegalovirus promoter. A total of 100 microg of purified plasmid DNA was injected intramuscularly in BALB/c mice three times at 14-day intervals. At 10 days after the second injection, the sera of the animals (100%) displayed significant antibody titers (by indirect immunofluorescence and fluorescence-activated cell sorter analysis) against syngeneic C26 cells transduced with FRalpha, but not against unmodified C26 cells. Immunoglobulin G2a was the predominant isotype. In addition, specific cytotoxic T lymphocyte activity against FRalpha-transduced C26 cells could be detected in splenocytes from all immunized animals. Coinjection of a plasmid containing interleukin-2 cDNA increased both antibody titers and cytotoxic T lymphocyte activity. Challenge by subcutaneous injection with FRalpha-transduced C26 cells (performed 10 days after the third injection) showed a statistically significant delay in tumor growth. Vaccination with the FRalpha and interleukin-2 cDNA mixture, which was performed after an intravenous injection of FRalpha-transduced cells, enhanced the mean survival time and reduced the number of lung metastases, thus suggesting that such vaccination is effective even against preexisting tumor cells.

Daily hunger sensation and body compartments: II. Their relationships in obese patients

Hunger sensation (HS) is a signal whose levels change during the 24-h day. The daily mean level of HS was correlated with the human body compartments, as investigated by bioelectrical impedance analysis, to detect the relationship between the orectic perception and both the free fat mass (FFM) and the fat body mass (FBM) in 22 clinically healthy subjects (CHS) (2 M, 20 W, BMI: 18.5-24.0 kg/m2) and 48 obese patients (OP) (4 M, 44 W, BMI: 25.2-54.7 kg/m2). In CHS, the daily mean level of HS correlated positively with the FFM and negatively with the FBM. These correlations were not present in OP. This lack of relationships between HS and the body compartments where energy is maximally consumed (i.e., the FFM) and maximally stored (i.e., the FBM) indicates that the orectic response to energy expenditure and the orectic inhibition to fat accumulation are feedback mechanisms which are impaired in obesity.

Daily hunger sensation and body composition: I. Their relationships in clinically healthy subjects

The human hunger sensation (HS) is a perceptive signal characterized by day-night variability (DNV). This pattern was investigated with respect to its relations with the body compartments in 22 clinically healthy subjects (CHS, 11 males and 11 females, mean age: 24 +/- 2.5 years, mean BMI: 21 +/- 1.7). The DNV was investigated by means of conventional descriptive statistics and the single cosinor method (SCM). Both procedures were applied to the orexigram, i.e., the 24-h profile of the orectic stimulus (OS) provided by each subject, who self-rated his/her HS (from 1 to 10 hunger units) every half hour. Body composition was investigated by Bioelectrical Impedance Analysis (BIA) on the day when the orexigrams were compiled. It was found that the daily HS level correlates positively with the Free Fat Body Mass (FFBM) and negatively with the Fat Body Mass (FBM). These opposite relations indicate that HS is stimulated by the needs of the FFBM, and inhibited by expansion of the FBM, and provide further evidence of the existence of an "adipostat" anorectic mechanism.

Hunger sensation: a chronobiometric approach to its within-day and intra-day recursivity in anorexia nervosa restricting type

Hunger sensation (HS) is a perception with a daily (circadian) and within-day (ultradian) recursive pattern. In human beings, circadian repeatability was investigated by means of the Single Cosinor method, while the ultradian recursivity was investigated by means of the spectral analysis, both applied to the 24-h HS profile (orexigram). Orexigrams were provided by each subject investigated, who self-rated her subjective orectic stimulus (OS) (from 1 to 10 hunger units) every half hour. The study was performed in 19 female patients aged 13-52 newly diagnosed as in the first episode of Anorexia Nervosa Restricting Type, with a BMI below 18.7. The control group consisted of 10 clinically healthy women aged 21 to 52 years with a BMI from 23 to 25. Two types of orexigrams were found. The first was characterized by a low profile with negligible ultradian variability, in which the HS circadian rhythm (CR) was still detectable, but the power spectrum (PS) was composed of unusual ultradian components associated with a very diminished amplitude for the circadian harmonics. The second was characterized by an almost regular profile, in which the ultradian variability was clearly detectable, the CR regularly fluctuated, and the PS was almost regularly composed. These findings indicate that anorectic patients (AP) can be recognized by their orexigram as "hyporectic", or "eurectic". Therefore, the term "anorexia" seems to be appropriate for AP who exhibit the first type of orexigram (anorectic aphagia nervosa), whereas the second identifying those who could be defined as suffering from "eurectic aphagia nervosa".

Point mutations in the tyrosine kinase domain release the oncogenic and metastatic potential of the Ron receptor

Ron (the receptor for Macrophage Stimulating Protein) has never been implicated before in human malignancies or in cell transformation. In this report we show that Ron can acquire oncogenic potential by means of two amino acid substitutions-D1232V and M1254T-affecting highly conserved residues in the tyrosine kinase domain. The same mutations in Kit and Ret have been found associated with two human malignancies, mastocytosis and Multiple Endocrine Neoplasia type 2B (MEN2B), respectively. Both mutations caused Ron-mediated transformation of 3T3 fibroblasts and tumour formation in nude mice. Moreover, cells transformed by the oncogenic Ron mutants displayed high metastatic potential. The Ron mutant receptors were constitutively active and the catalytic efficiency of the mutated kinase was higher than that of wild-type Ron. Oncogenic Ron mutants enhanced activation of the Ras/MAPK cascade with respect to wild type Ron, without affecting the JNK/SAPK pathway. Expression of Ron mutants in 3T3 fibroblasts led to different patterns of tyrosine-phos-phorylated proteins. These data show that point mutations altering catalytic properties and possibly substrate specificity of the Ron kinase may force cells toward tumorigenesis and metastasis.

Limiting dilution analysis of peripheral blood lymphocytes reacting with non-small-cell lung cancer: functionally heterogeneous effectors efficiently lyse autologous cancer cells

It has recently been shown that the infusion of tumor infiltrating lymphocytes (TIL) and recombinant interleukin-2 (rIL-2) in patients operated on for advanced non-small-cell lung cancer (NSCLC), has significant effects in terms of the survival time and control of local relapses. Despite the evident clinical effects, the treatment is unavailable for patients in which TIL have lost their proliferative potential. In an attempt to identify new sources of effector cells using mixed lymphocyte/tumor cultures (MLTC), populations of peripheral blood (PB) lymphoid cells, which have the capability of lysing autologous NSCLC, were studied at the clonal level. Specific cytolytic lymphocytes were detected at very low frequencies in two out of four patients, whereas non-MHC restricted cytolytic T cells were frequently detected. Cytolytic CD4+ belonged to the Th0 or Th2 subsets and were characterized by cytokine secretion patterns suggestive of a lymphokine cascade that could be involved in cancer control. The identification of different efficient effector mechanisms at the clonal level strongly supports the use of in vitro activated lymphocytes, derived from PB, in protocols of adoptive immunotherapy in patients with advanced NSCLC in which TIL are unavailable.

p49, a putative HLA class I-specific inhibitory NK receptor belonging to the immunoglobulin superfamily

NK cells display several killer inhibitory receptors (KIR) specific for different alleles of MHC class I molecules. A family of KIR are represented by type I transmembrane proteins belonging to the immunoglobulin superfamily (Ig-SF). Besides cDNA encoding for these KIR, additional cDNA have been identified which encode for Ig-SF receptors with still undefined specificity. Here we analyze one of these cDNA, termed cl.15.212, which encodes a type I transmembrane protein characterized by two extracellular Ig-like domains and a 115-amino acid cytoplasmic tail containing a single immuno-receptor tyrosine-based inhibitory motif (ITIM) which is typical of KIR. cl.15.212 cDNA displays approximately 50 % sequence homology with other Ig-SF members. Different from the other KIR, cl.15.212 mRNA is expressed by all NK cells and by a fraction of KIR+ T cell clones. cl.15.212 cDNA codes for a membrane-bound receptor displaying an apparent molecular mass of 49 kDa, thus termed p49. To determine the specificity of the cl.15.212-encoded receptor, we generated soluble fusion proteins consisting of the ectodomain of p49 and the Fc portion of human IgG1. Soluble molecules bound efficiently to 221 cells transfected with HLA-G1, -A3, -B46 alleles and weakly to -B7 allele. On the other hand, they did not bind to 221 cells either untransfected or transfected with HLA-A2, -B51, -Cw3 or -Cw4. The binding specificity of soluble p49-Fc was confirmed by competition experiments using an anti-HLA class I-specific monoclonal antibody. Finally, different cDNA encoding for molecules homologous to cl.15.212 cDNA have been isolated, two of which lack the sequence encoding the transmembrane portion, thus suggesting they may encode soluble molecules.

TIMP-2 over-expression reduces invasion and angiogenesis and protects B16F10 melanoma cells from apoptosis

The matrix metalloproteinase (MMP) inhibitor TIMP-2 has a high specificity for gelatinase A/MMP-2. An imbalance between gelatinase A and TIMP-2 in favor of enzymatic activity is linked to the degradation of the extracellular matrix (ECM) associated with several physiologic and pathologic events, including angiogenesis, invasion and metastasis. Since TIMPs are secreted molecules, they have the potential to be used for gene therapy of certain tumors. We transfected B16F10 murine melanoma cells, a highly invasive and metastatic cell line, with an expression vector harboring a cDNA encoding for human TIMP-2. The clones obtained were isolated and examined for TIMP-2 over-expression and changes in tumor cell phenotype. The amount of recombinant TIMP-2 produced correlated with a reduction in invasion. In an in vivo angiogenesis assay, TIMP-2-transfected clones showed reduced levels of blood vessel formation, and in vitro conditioned media from TIMP-2 transfectants showed diminished induction of endothelial cell migration and invasion. TIMP-2 over-expression limited tumor growth in vivo and neoangiogenesis when cells were injected subcutaneously in mice in the presence of Matrigel. However, TIMP-2 overexpressing clones were found to be more resistant to apoptosis than parental and control melanoma cells, while necrosis was increased. Our data confirm the role of TIMP-2 in the down-regulation of metastasis and angiogenesis but indicate a possible involvement in tumor cell survival.

TIMP-2 over-expression reduces invasion and angiogenesis and protects B16F10 melanoma cells from apoptosis

The matrix metalloproteinase (MMP) inhibitor TIMP-2 has a high specificity for gelatinase A/MMP-2. An imbalance between gelatinase A and TIMP-2 in favor of enzymatic activity is linked to the degradation of the extracellular matrix (ECM) associated with several physiologic and pathologic events, including angiogenesis, invasion and metastasis. Since TIMPs are secreted molecules, they have the potential to be used for gene therapy of certain tumors. We transfected B16F10 murine melanoma cells, a highly invasive and metastatic cell line, with an expression vector harboring a cDNA encoding for human TIMP-2. The clones obtained were isolated and examined for TIMP-2 over-expression and changes in tumor cell phenotype. The amount of recombinant TIMP-2 produced correlated with a reduction in invasion. In an in vivo angiogenesis assay, TIMP-2-transfected clones showed reduced levels of blood vessel formation, and in vitro conditioned media from TIMP-2 transfectants showed diminished induction of endothelial cell migration and invasion. TIMP-2 over-expression limited tumor growth in vivo and neoangiogenesis when cells were injected subcutaneously in mice in the presence of Matrigel. However, TIMP-2 overexpressing clones were found to be more resistant to apoptosis than parental and control melanoma cells, while necrosis was increased. Our data confirm the role of TIMP-2 in the down-regulation of metastasis and angiogenesis but indicate a possible involvement in tumor cell survival.

Circulating endothelin-1 in non-insulin-dependent diabetic patients with retinopathy

Endothelin-1 (ET-1), a novel 21-amino acid vasoconstrictive peptide secreted by endothelial cells, has been thought to play a role in various forms of vascular disease. Diabetes mellitus is well known for its association with microvascular damage. To investigate whether ET-1 levels may be related to microangiopathy in diabetes mellitus, plasma ET-1 levels were measured in two groups of diabetic patients: A) 47 patients with non-insulin dependent diabetes mellitus (NIDDM) and retinopathy (28 M, 19 F; mean age 60.7+/-8.5 yrs) but without nephropathy (microalbuminuria < 30 mg/day) and hypertension (SBP < 140, DBP < 90 mmHg); group A was divided in three subgroups based on the severity of retinopathy: a) 16 with background retinopathy; b) 21 with pre-proliferative retinopathy; c) 10 with proliferative retinopathy. B) 8 patients with insulin-dependent diabetes mellitus (IDDM) recently diagnosed (6 M, 2 F; 16.4+/-3.8 yrs) without complications. C) 28 healthy subjects (HS) (16 M, 12 F; 47.8+/-11.8 yrs) as controls. In the NIDDM group the ET-1 concentration was significantly higher (17.3+/-2.4 pg/ml) than both in the HS (8+/-4.7 pg/ml) and IDDM patients (10.2+/-3.7 pg/ml) (p < 0.0001). In the subgroups with retinopathy the ET-1 levels were a) 15.1+/-4.3 pg/ml; b) 22.2+/-6.8 pg/ml and c) 16.6+/-5.1 pg/ml. These values were significantly elevated as compared to HS (p<0.001; p < 0.0001; p < 0.002, respectively), being the highest levels of ET-1 observed in the NIDDM patients with pre-proliferative retinopathy. In conclusion our study revealed that the ET-1 concentrations are elevated in NIDDM patients with retinopathy especially in those patients with pre-proliferative retinopathy.

Clonal analysis of stably transduced human epidermal stem cells in culture

We have transduced normal human keratinocytes with retroviral constructs expressing a bacterial beta-galactosidase (beta-gal) gene or a human interleukin-6 (hIL-6) cDNA under control of a long terminal repeat. Efficiency of gene transfer averaged approximately 50% and 95% of clonogenic keratinocytes for beta-gal and hIL-6, respectively. Both genes were stably integrated and expressed for more than 150 generations. Clonal analysis showed that both holoclones and their transient amplifying progeny expressed the transgene permanently. Southern blot analysis on isolated clones showed that many keratinocyte stem cells integrated multiple proviral copies in their genome and that the synthesis of the exogenous gene product in vitro was proportional to the number of proviral integrations. When cohesive epidermal sheets prepared from stem cells transduced with hIL-6 were grafted on athymic animals, the serum levels of hIL-6 were strictly proportional to the rate of secretion in vitro and therefore to the number of proviral integrations. The possibility of specifying the level of transgene expression and its permanence in a homogeneous clone of stem cell origin opens new perspectives in the long-term treatment of genetic disorders.

Ligand-independent tyrosine phosphorylation of the receptor encoded by the c-neu oncogene

Incubation of Swiss 3T3 murine fibroblasts at low temperatures induces phosphorylation on tyrosine of a transmembrane protein of 175 kDa. This phenomenon is time and temperature dependent and reaches a maximum after 2 hr at 4 degrees C. The 175 kDa protein phosphorylated in vivo at low temperatures can be immunoprecipitated by phosphotyrosine antibodies and displays auto-kinase activity in vitro in the presence of radiolabelled ATP. This molecule was found to react with anti-peptide antibodies directed against the product of the HER2/neu proto-oncogene only when immunoprecipitated with phosphotyrosine antibodies from cold-stimulated cells. Activation of protein kinase-C by treatment of the cells with phorbol esters, bombesin or PDGF inhibits the effect of the exposure to low temperatures. Phosphorylation of p175 is not induced by treatment of the cells with the phosphatases inhibitor sodium orthovanadate. These results suggest that, at low temperatures, the tyrosine kinase associated with the putative receptor encoded by c-neu is activated by physico-chemical modifications of the plasma membrane.

Neuromagnetic topography of photoconvulsive response in man

The neuromagnetic method was applied to the study of photoconvulsive responses. The identification of specific magnetic field distributions over the scalp was achieved by; (a) a stimulation paradigm consisting of series of trains of flicker stimuli randomly presented to the epileptic patient, after eye closure, to get epileptic responses while avoiding seizures; (b) a novel procedure for data analysis, to select consistent responses. These patterns, when sufficiently stable in time and dipolar in shape, were used for source localization in the usual biomagnetic framework of the equivalent current dipole source representation. The results of this approach suggest that different specific cortical areas are repeatedly and randomly activated, involving mainly the frontal, occipital and temporal areas, often with a hemispheric prevalence.

Short latency somatosensory evoked responses to median nerve stimulation in healthy humans: electric and magnetic recordings

Somatosensory Evoked Potentials (SEPs) and Somatosensory Evoked magnetic Fields (SEFs) to median nerve stimulation at wrist were recorded in 5 healthy subjects and the components between 15 and 30 ms after the stimulus were evaluated on the hemiscalp contralateral to the stimulated wrist. SEPs were measured by means of a 32-channel recorder and compared with SEFs obtained via multiple measurements with a 4-channel sensor. Equivalent dipole localization was carried out for the magnetic components peaking at about 15, 20 and 24 ms. The scalp distribution of SEPs, illustrated by bit mapped color images, were qualitatively explained by three separate sources. The first is described as a tangentially oriented dipole placed behind the Central Sulcus and responsible for the parietal N20-"late P25" waves and for the frontal P20-N30 ones. The second is represented by a radieal dipole placed just in front of the Central Sulcus and pointing towards the motor strip, responsible for the rolandic P22 component. The third is just behind the Central Sulcus and is radieally oriented towards the surface of the postcentral sensory area for the "early P25" parietal wave. The SEFs distributions, illustrated by color isofield contour maps, were quantitatively explained by a unique tangential dipole localized, with good resolution, well behind the Sulcus for the 15 ms waves and slightly frontal to this site for the waves peaking at around 20 and 24 ms. The equivalent dipole has been localized at a depth of about 5 cm (15 ms component), 2 cm (20 ms components) and 4 cm (24 ms component), across the studied subjects. It is stressed that the dipole responsible for the magnetic pattern is likely to be the same tangential dipole responsible for a part of the electric pattern. Due to their radieal orientation, the other two dipoles, proposed for the SEPs maps, would be mostly undetectable by a magnetic investigation.

A tyrosine protein kinase activated by bombesin in normal fibroblasts and small cell carcinomas

In Swiss 3T3 fibroblasts, antibodies which recognize a phosphotyrosine residue (P-Tyr antibodies) identify a 115-kDa cell surface protein (p115) that becomes phosphorylated on tyrosine as a response to bombesin stimulation of quiescent cells. The extent of phosphorylation is dose-dependent and correlates with the mitogenic effect induced by bombesin, measured by [3H]thymidine incorporation. Tyrosine phosphorylation of p115 is detectable minutes after addition of bombesin and precedes the activation of c-fos and c-myc gene transcription. Immunocomplexes of phosphorylated p115 with P-Tyr antibodies bind 125I-labeled [Tyr4]bombesin in a specific and saturable manner and display an associated tyrosine protein kinase activity enhanced by bombesin. P-Tyr antibodies also recognize a protein of 115 kDa, phosphorylated at tyrosine, in four human SCLC lines producing bombesin but not in a non-producer "variant" line. Phosphorylation of SCLC p115 does not require the addition of exogenous bombesin. As in the case of the p115 immunoprecipitated from mouse fibroblasts, the SCLC p115 is phosphorylated in an immunocomplex kinase assay. These observations are in agreement with the hypothesis of autocrine activation of bombesin receptors in human small cell lung carcinoma cells.