The role of kallikreins in growth factor processing: the kallikrein gene family from the African rodent Mastomys

1. Kallikreins are trypsin-like serine proteases which have been implicated in the biosynthesis of a number of growth factors and hormones. Mastomys, an African rodent, is the only mammal other than mouse known to contain high levels of kallikreins and growth factors in its submandibular gland. Mastomys has a large kallikrein family similar to mouse and rat. Cloning and sequencing of several of these cDNAs demonstrates a high degree of homology with mouse and rat kallikreins, but careful analysis suggests that it will not be possible to determine the function of these kallikreins by sequence information alone. 2. It is not known whether a Mastomys kallikrein processes and binds to nerve growth factor (NGF) as in mouse submandibular gland. Mastomys NGF is bound to a protein similar in size, charge, and lack of esterase activity to alpha-NGF, a mouse kallikrein. However, the Mastomys NGF complex does not contain a proteolytically active kallikrein as does the mouse NGF complex. Thus, the identification of kallikreins as growth factor processing enzymes and the presence of a kallikrein family member in high-molecular-weight complexes in species other than mouse is still in question.

Characterization of kallikrein cDNAs from the African rodent Mastomys

Kallikreins comprise a family of serine proteases that are required for the processing of hormone precursors, thereby controlling many physiological processes including blood flow, ion transport, and inflammation. In rodents such as mouse, rat, and Mastomys, many kallikreins are expressed in the submandibular gland (SMG), but only a limited number, notably true tissue (glandular) kallikrein, are expressed in the kidney. We report here the cloning and characterization of kallikrein cDNAs from the Mastomys SMG. Two of these are expressed in the kidney as well as in the SMG, and one may code for the true tissue kallikrein of Mastomys. A third kallikrein is expressed only in the SMG and bears some resemblance to a murine nerve growth factor-associated protein. The existence of a family of Mastomys SMG kallikreins suggests that these enzymes act as prohormone-processing enzymes in Mastomys. DNA sequence analysis and hybridization studies demonstrate that, although Mastomys kallikreins are very similar in structure to both mouse and rat kallikreins, their expression patterns differ. The expression of more than one Mastomys glandular kallikrein in the kidney is similar to that in the rat, but the sequence and nonsexually dimorphic expression of the putative tissue kallikrein most closely resembles mouse. Mastomys represents an interesting hybrid between mouse and rat, providing an important animal model for studies of kallikrein expression and regulation.

Greenland Ice Sheet Surface Properties and Ice Dynamics from ERS-1 SAR Imagery

C-band synthetic aperture radar (SAR) imagery from the European Space Agency's ERS-1 satellite reveals the basic zonation of the surface of the Greenland Ice Sheet. The zones have backscatter signatures related to the structure of the snowpack, which varies with the balance of accumulation and melt at various elevations. The boundaries of zones can be accurately located with the use of this high-resolution imagery. The images also reveal a large flow feature in northeast Greenland that is similar to ice streams in Antarctica and may play a major role in the discharge of ice from the ice sheet.

Nerve growth factor synthesis by mouse submandibular gland cells in culture

Mouse submandibular gland (SMG) cells in culture rarely retain functional properties of SMG cells in vivo. We demonstrate that both primary SMG cells and the mouse SMG cell line SCA-9 secrete biologically active nerve growth factor (NGF). However, primary cells secrete 40-fold more NGF than SCA-9 cells, demonstrating that SCA-9 cells cannot substitute for primary SMG cells for the study of SMG NGF in vitro.

beta-NGF-endopeptidase: structure and activity of a kallikrein encoded by the gene mGK-22

Mouse nerve growth factor (NGF) is cleaved at a histidine-methionine bond to release an NH2-terminal octapeptide (NGF1-8). The enzyme responsible, beta-NGF-endopeptidase, is structurally and functionally similar to gamma-NGF and epidermal growth factor-binding protein (EGF-BP) and cleaves mouse low molecular weight kininogen to produce bradykinin-like activity. These data have suggested that, like gamma-NGF and EGF-BP, beta-NGF-endopeptidase is a mouse glandular kallikrein. Evidence for a physiological role for NGF1-8 encouraged studies to further characterize the structure and function of this enzyme. Purified beta-NGF-endopeptidase migrated as a single band on isoelectric focusing and reducing SDS-polyacrylamide gels. As was expected, it removed NGF1-8 from NGF. Interestingly, enzymatic activity on an artificial substrate, and on NGF, was inhibited by NGF1-8 and by bradykinin. These studies further supported the view that beta-NGF-endopeptidase acts on both NGF and kininogen. The first 30 NH2-terminal amino acids of beta-NGF-endopeptidase were sequenced. This analysis demonstrated that the enzyme is encoded by the gene designated mGK-22 (Evans et al., 1987). The sequence of this gene corresponds to that of EGF-BP type A (Anundi et al., 1982; Drinkwater et al., 1987), and so studies were performed to determine whether or not beta-NGF-endopeptidase participates in EGF complex formation. Chromatographic and kinetic data gave no evidence that beta-NGF-endopeptidase is an EGF-binding protein. Our studies suggest that contamination of high molecular weight (HMW) EGF preparations with beta-NGF-endopeptidase erroneously led to earlier designation of the product of mGK-22 as an EGF-BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure and biosynthesis of nerve growth factor

Most of our knowledge about NGF comes from extensive study of the mouse submaxillary gland protein. NGF from this source is isolated as a high molecular weight complex consisting of beta-NGF and two subunits, alpha and gamma, belonging to the kallikrein family of serine proteases. There are few other tissues where NGF is found in sufficient quantities for protein purification and study, although new molecular biological techniques have accelerated the study of NGFs from a variety of species and tissues. Mouse submaxillary gland NGF is synthesized as a large precursor that is cleaved at both N- and C-terminals to produce mature NGF. This biologically active molecule can be further cleaved by submaxillary gland proteases. The roles of the alpha and gamma subunits in the processing of the beta-NGF precursor, the modulation of the biological activity of beta-NGF, and the protection of mature beta-NGF from degradation have been well studied in the mouse. However, the apparent lack of alpha and gamma subunits in most other tissues and species and the existence of a large family of murine kallikreins, many of which are expressed in the submaxillary gland, challenge the relevance of murine high molecular weight NGF as a proper model for NGF biosynthesis and regulation. It is important therefore to identify and characterize other NGF complexes and to study their subunit interactions, biosynthesis, processing, and regulation. This review points out a number of other species and tissues in which the study of NGF has just begun. At this time, there exist many more questions than answers regarding the presence and the functions of NGF processing and regulatory proteins. By studying NGF in other species and tissues and comparing the processing and regulation of NGF from several sources, we will discover the unifying concepts governing the expression of NGF biological activity.

Physical Conditions at the Base of a Fast Moving Antarctic Ice Stream

Boreholes drilled to the bottom of ice stream B in the West Antarctic Ice Sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1.6 bars of the ice overburden pressure. These conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick. The mechanics of ice streaming plays a role in the response of the ice sheet to climatic change.

Molecular cloning of a cDNA encoding the nerve growth factor precursor from Mastomys natalensis

Mastomys natalensis is an African rat that has high levels of nerve growth factor (NGF) in its submaxillary glands. Like in the mouse, Mastomys NGF is found as a high-molecular-weight complex. However, the Mastomys complex differs from the mouse complex, in that the gamma-subunit is either missing or is less tightly bound in the Mastomys NGF complex. In the mouse, the gamma-subunit has been implicated in the processing of the beta-NGF precursor. The possible lack of gamma-subunits in the Mastomys NGF high-molecular-weight complex suggested that the Mastomys beta-NGF precursor might differ from the mouse beta-NGF precursor in some of its processing sites. In particular, Mastomys beta-NGF might lack the C-terminal dipeptide cleavage site implicated in beta-gamma subunit interactions in mouse NGF. In order to test this hypothesis, we isolated and sequenced a cDNA clone for Mastomys beta-NGF. We report here the cloning and sequencing of a cDNA coding for beta-NGF from Mastomys natalensis. The cDNA library was prepared from Mastomys submaxillary gland mRNA and the beta-NGF clone was isolated using a mouse cDNA as a probe. The nucleotide sequence of Mastomys beta-NGF is 95% homologous to that of mouse beta-NGF. In particular, the Mastomys beta-NGF precursor contains the same three C-terminal residues as the mouse, suggesting that the Mastomys beta-NGF precursor could interact with a gamma-like subunit.(ABSTRACT TRUNCATED AT 250 WORDS)

The high molecular weight nerve growth factor complex from Mastomys natalensis differs from the murine nerve growth factor complex

Both the male and the female of Mastomys natalensis, an African rat, have high levels of nerve growth factor (NGF) in their submaxillary glands. Mastomys high molecular weight (HMW) NGF was purified by gel filtration and ion-exchange chromatography and was compared with HMW NGF from the male mouse submaxillary gland. Mastomys HMW NGF sediments as a 5S species, does not exhibit esterase activity, and is more difficult to dissociate at acid pH than mouse 7S NGF. The biological activity could be isolated as a purified Mastomys beta NGF protein identical in size and charge with that purified from male mice. The N-terminal amino acid sequence of the first 20 residues was determined and found to differ from that of mouse only at residue 8. Western blotting of Mastomys 5S NGF using antiserum against mouse beta NGF indicates that the beta NGF subunit of Mastomys is very similar to that of the mouse. Southern blots using a mouse kallikrein probe also demonstrate the presence of a large kallikrein family in Mastomys similar to that in mouse, and Northern blots verify transcription of kallikreins in Mastomys submaxillary gland. SDS-PAGE and isoelectric focusing gels reveal a Mastomys subunit that comigrates with mouse alpha subunit. However, neither oligonucleotide probes directed against mouse alpha subunit RNA nor antibodies directed against mouse alpha NGF cross-react strongly with the Mastomys material. This indicates that the second subunit of the Mastomys complex is not very similar to the mouse alpha subunit.

The NGF and kallikrein genes of mouse, the African rat Mastomys natalensis and man: their distribution and mode of expression in the salivary gland

The kallikrein genes and their expression in the salivary glands of mouse, the African rat Mastomys natalensis and human were compared. The Mastomys kallikrein genes comprise a family of genes similar to those of mouse. Androgen markedly enhances transcription of glandular nerve growth factor (NGF) and kallikrein in both male and female Mastomys suggesting the presence of testosterone regulated kallikrein genes for growth factor precursor-processing in both sexes. In contrast, although a kallikrein transcript was detected in human salivary glands of the same size as the mouse or Mastomys transcript no difference in the amount of transcript was seen in adult male or female. The absence of kallikrein genes regulated by testosterone and of NGF transcripts in the human implies that there is no human equivalent of the mouse salivary 7S NGF complex.

Iodination of the progesterone receptor from hen oviduct spares the DNA-binding domain

The progesterone receptor from hen oviduct is isolated as a complex of two subunits, A and B. The A protein binds one molecule of progesterone and also binds to DNA with high affinity. The native A protein can be labeled with iodine with no loss of DNA-binding activity. Limited Staphylococcus aureus V8 protease digestion of the labeled preparation results in a number of DNA-binding and non-DNA-binding fragments of the receptor. The progesterone-binding domain contains iodine label. However, two low-molecular-weight DNA-binding fragments do not contain iodine label, indicating a lack of susceptible tyrosine residues near the DNA-binding site of the native receptor. The labeled receptor and its fragments will facilitate studies of the isolated DNA-binding and progesterone-binding domains of the hen A protein as well as of the activity of the native receptor in the presence and absence of hormone.

The sequence of a cDNA clone coding for a novel kallikrein from mouse submaxillary gland

Mouse submaxillary gland contains many proteolytic enzymes, the most widely studied of which are the kallikreins. This gland also contains high levels of nerve growth factor (NGF), which is isolated as a complex of three subunits, alpha, beta, and gamma. We report here the cloning and sequence analysis of a novel kallikrein from mouse submaxillary gland. Antibodies directed against the alpha subunit precipitate the product of this clone, but do not precipitate the homologous gamma subunit. This new kallikrein is therefore closely related to alpha NGF, yet in contrast to the alpha subunit, its sequence suggests it has proteolytic activity.

Control of the receptor for galactose taxis in Salmonella typhimurium

The chemotactic response to galactose in wild-type Salmonella typhimurium is not inducible by galactose, but is inducible by fucose, a non-metabolizable analog. In a galactokinase mutant, however, the galactose receptor is inducible by galactose. These data indicate that the concentration of free galactose in the cell controls the levels of the galactose receptor. The intensities of the chemotactic responses were found to vary in proportion to the concentration of galactose receptors. In bacteria with higher levels of galactose receptors, the ribose response is inhibited by galactose. This supports the model in which the ribose and galactose receptors compete for a common component of the signaling system.