Characterization of the Structure and Function of a Novel MAP Kinase Kinase (MKK6)

Abstract

Mitogen-activated protein (MAP) kinases require dual phosphorylation on threonine and tyrosine residues in order to gain enzymatic activity. This activation is carried out by a family of enzymes known as MAP kinase kinases (MKKs or MEKs). It appears that there are at least four subgroups in this family; MEK1/MEK2 subgroup that activates ERK1/ERK2, MEK5 that activates ERK5/BMK1, MKK3 that activates p38, and MKK4 that activates p38 and Jun kinase. Here we describe the characteristics of a new MKK termed MKK6. The clones we isolated encode two splice isoforms of human MKK6 comprised of 278 and 334 amino acids, respectively, and one murine MKK6 with 237 amino acids. Sequence information derived from cDNA cloning indicated that MKK6 is most closely related to MKK3. The functional data revealed from co-transfection assays suggests that MKK6, like MKK3, selectively phosphorylates p38. Unlike the previously described MKKs (or MEKs), MKK6 exists in a variety of alternatively spliced isoforms with distinct patterns of tissue expression. This suggests novel mechanisms regulating activation and/or function of various forms of MKK6.

Phenotype-assisted transcriptome analysis identifies FOXM1 downstream from Ras–MKK3–p38 to regulate in vitro cellular invasion

“…The constitutively active MKK3-expressing construct has been described elsewhere (Han et al, 1996;Jiang et al, 1996) and mock control was prepared using the empty vector (pcDNA3). For reporter-gene assays 1 mg of empty vector or reporter-gene vector encoding the FoxM1 promoter in front of the luciferase gene (Korver et al, 1997;Laoukili et al, 2005) were transfected into the respective cell lines or cotransfected with the constitutively active MKK3 expression construct using the JetPrime reagent (PeqLab, Erlangen, Germany) at a 1:1 ratio.…”

Signaling by dual specificity kinases

“…MEKK1 does not activate MKK3 . Similarly, The small GTPases such as Rac and CDC 42 fail to activate MKK3 (Han et al, 1996). However, the recently identi®ed MKKKs such as apoptosis signal regulating kinase or ASK1 (Ichijo et al, 1997), MEKK4/MTK1 (Takekawa et al, 1997), TGFbactivated kinase-1 or TAK1 (Shirakabe et al, 1997) and mixed lineage kinase-3 or MLK3 (Rana et al, 1996;Tibbles et al, 1996) appear to activate MKK3.…”

“…The dual speci®city kinase that phosphorylate ERK5 is known as MEK5 or MKK5 (Zhou et al, 1995;. The recently identi®ed dual speci®city kinase that speci®cally involved in the regulation of p38MAPK is known as MKK6 (Raingeaud et al, 1996;Moriguchi et al, 1996;Han et al, 1996;Stein et al, 1996). Likewise, newly characterized dual specificity kinase that speci®cally activates JNK through phosphorylation is named MKK7 Yao et al, 1997;Tournier et al, 1997;Wu et al, 1997).…”

p38 protects human melanoma cells from UV-induced apoptosis through down-regulation of NF-κB activity and Fas expression

“…The expression constructs, pcDNA3-FLAG-MKK7b1 (Tournier et al, 1999), pcDNA3-JNK1-APF (Butter®eld et al, 1997) p38-ASP (Enslen et al, 1998) MKK6-DD (Han et al, 1996), and ASK1DN (Saitoh et al, 1998) were also used in these experiments. Luciferase activity was determined using the Luciferase assay system from Promega (Madison, WI, USA) and normalized based on b-galactosidase levels in transfected cells.…”