Negative signaling in B cells: SHIP Grbs Shc

IMMUNOLOGY

Tf)DAY

egative signaling in B cells: SHIP Grbs She Susheela Tridandapani, Todd Kelley, Damon

Cooney, Madhura Pradhan

and K. Ma& Coggeshall Negotiue sigtznlr~~girz B cells IS

ofrlic

rrritinfed by/ cc-crosslinking

mtrgtw receptor receptor, resultrq

md the Fey in ces_dio,r

of

B-celisipfiq tmfzfsma?,ii1 signaling

events

in pmliferation

and

antigen-specific

Ig. The activation

is regxdated interaction

sarehan

at several of B 4s

lymphokines ation

and

with

that promote

dntigen-specitic

pressive

of B-cell aclivahon:

secretion

and bear a” intact

suppressive

effect of soluble

antibodies

the Fq receptor support

Ig (reviewed qnaIing

with FqRII

indicate

that it

xtivation

negative Ig must

signahng. and

The observation

A (Ref. 5) established signaling.

signaling

by miuble,

physiological

positive nistic

anhgn-sp+xIftc

pmcess

probably

or anti-idiotyprc

BCR, implying

signaling model

ccqxxates

Following

datting,

protein

7AP-7O/Syk

pnorytate

anhgen

tymsine

and then outline a mecha-

of negative exiting

qnaling

new

that in-

findings

into

the

k”owh?dge.

several

fzmihs

Once

pmteins,

which **en ass&ate

that serves to prevent

activated,

these

activate

those of the Src enzymes

phos-

n”ncovaIentIy

via

WIW, SH3 and plecksbin-homology

(PHJ domain&‘“.

PTK sub-

anti-Fc-

strates t” lymphocytes

with a consened

sequence of

lend

of src-homology

a”li”o aads

2 (SH2).

include pmte’ti

Ig to suppress

pears to act as a scat%Id for a multilayered

F&II

signaling

is a

excess Ig production.

inductmn

When phosphorylated

biochemical

of “ascent gene expressIon proteins

subunits

activation of antigen

tp

on k-y tymsine resrdues, the ITAM ap-

The SH2domain-contaiiing sgxaling

ty”al&ased

found in signaling

ceptas.

in D;U~

phosphotyrosine-bmdiig

know” as the i”l”“moreceptor

mobf (ITAM) CR& ll-13).

the BCR 1s C(F

occurs

of lymphocytes

that the a role for

Ig crosslinks

that negahve

receptors

Iunases WTKs), SpecificaIIy

te”x that activate sawaI

and the antigen-bound

bn-

are dear, its

interactions

These hndmgs

in which

of the BCR and FqRII

when secreted antigen-specific

the effects and

sigttafing

specific

pmduction.

Co-cmssIIIng

While

Positive signaling several and

PXIVZ-

bind

Ig was blodced by neutralizing

in negative

and

in Ref. I). This sup

by PhdIips

Fc domain.

and by protein

(F&II)

mice,

role expwinwnts

suppressive

to a model of negative

cmsslinked antibody

soluble,

anti-Fc

FcyRII-deficient

of negative

b&y of existing

Ig has been termed

on “egahve that

of

flctiitntiorz I)I B cells.

to anhgen-triggered

of “ascent

effect of soluble

portance

secreted,

less responsive

Eariy studies

receptor

Siirly,

on

biochtical basis is not well understood. Thii arti& wiiI first describe key events in

proteins thnt lend to Rm

Ig-secreting

Ig plays a” important

B 4s

demonstrated antigen

of

is po-

by an autoimmune

and

IgG anhMi&.

for

She with the GrbZ-Sos complex

T c&s,

B-cell pmIiferinto

B &Is.

~II the regxdahon subsequent

helper

role 1s proposed

on rheumatoid signaling

which exhl%it an increase in antigenqwxific

SHIP irr blocking the ivteructior; of

the

negative

antibodyh

mtibody secretion. Here, LI

cornpeltfrve

pmclzss

and _cretion

differentiation

c&I or memory

renders

of soluble

IeveIs, in&ding

as well as the fornation

od

that result

by studies

in which

te”tiaIIy blocked

twn,hrhibiting B-cell prolifemtim duces positive

This IS supported arthritis

that are found

with ITAMS (Refs M-17). Although

assembly of signaling

pathways,

cubninating

pm in the

and entry into the c&I cyde.

adaptor directly

pmt.zin She is among or indirectIy

details of Ras activahon

the

complrxed in BceIIs

P i: 1‘,*=“011 11

are lack&.

membrane

recmitment

and subsequent

phosphoryl-

ation of She at tyrosine residues Y239, YWJ or Y317 (Ref. 18) m SW-

’

(a)

Fe@ piTiM

I

SHIP

She

era1 cell activation models promotes the association of the CrbZ-SOS complex of proteins which, in turn, catalyzes (Ref. 19). Triggering

of the BCR on 6 c&s

to induce

phosphorylation

This

tymsine

protein

has

recently

domainiontaining with a “lrmber

the activahon of Xas

I-as also been reported

of a -145

been

identified

inositol polyphosphate of stmch”aI

feature

kDa

protcin’J2’.

as a novel

SH2-

5phosphatase

suggesting

(SHIP)

interactions

with

I

other proteins, including hvo NPxY motifs; when phosphotyhted, these mot& act as Iigands for l’fB domains’2-Z’. SHIP occurs in

that appear

three forms - ~145 p13S and pIlO tivc splicing

of a single mRNA transcript2’.

forms contain

a” N-taninal

SHIP has bee” repotted of mammalian

to be complexed

celIs with various

SHIP I” signal transduction memIx

cytokln&~.

eff&

athough

is not known. kly

to1 1,4,5trisphosphate suggeshng

phosphatase

naling

events

associated with

located

experiments

signe!iog.

by cwligation

a qumxnent

in a” show”

that

proposed

of FqRll

InhIbihon

that negative

(Ref. 31). It has SH2domain-

from the mouse

by co-crosslinking

strain

results

is required

Consequently,

from

to

of FcyRIl and

that SHP-1 expression

of SHIP (see above) and its association

phosphorylation

3oth events were blocked by pre-treamtent

known

I” SHP-I, were show”

of B-cell achvation.

signahng

motif

(SHP-I; previously

defiaent

signal triggered

the BCR (Ref. 32). suggesting

have

of Y309

inhibition

ITIM binds

B cells derived

rno~1wzztnr,which are geneticaIIy lack the Inhibitory

phosphoqlation

do-

phosphataw

as PTPICkQ. Forthennore.

pn sig-

of the BCR and FqRII

the phosphorylated

phosphotymsine

FcyRll-ma&ted

C !PLC) activity repre-

tyroGn&awI

(ITIMJ’2 wxthtn the Intracellular been

containing

for this

More recent studies

for tyrosme

bnnwnoreceptor

mechanism

reported inhibition of inosi-

formation and caldum tlw?=‘,

of phospholfpaw

of negative

initiated

demonshated

effects on Ras for this appar-

fanxiI~“2x.

the biochemicJ

[lns(1,4~)P:

that izbition

sents one outcomt

The role played by

have been proposed

of the inmitol

conditions,

pIlO does not2l.

with She upon stimulaho”

is signalilg

while

IS not yet known, although

activity and phosphatidyIinosito1 entty unique

to arise by altema-

Thus, the ~145 and ~135

SH2 domain,

for

it was

ITlM phosphoryl-

monoclonal

antibody,

the induction

indicating

of these events.

gard mdlcated

that FqRll

while transfection

and SHIP-She

that SHIP, in addition

to SHP-I, might

signaling

into the LKR slgnahng

complex

posed that the catalytic

activity

conhibution

sigrabng.

have

demonstrated

phosphorylated promote

Im(1,4,5)P,

rapid

concept,

sip”.&@,

recent

de-phosphorylation

PLCy2 in B cells stimulated

negative

is a substrate for previous

the

of this

suggesting

under

stud&

of tyrosint~ conditions

the possibility

that

that PLCy2

for SHP-I. This finding also provider. an explanation observatiom

demonstrating

IeveIs in B celIs activated

the transient

under

elevahon

of

aim&w co”dltionr4”.

by blnding

interactions

role in negative of Ras activity

signaling observed

The molecular

negative

but not positive

signaling

3hhave revealed

condxhons promoted

that

tyrosine

SH2 dolnain

Here, it 1s further

negative

and 1s potentially

phosphorylation She contains

act as ligands

SEPTEMBER

that active

(see below). between

SHIP

complex.

Al-

on She are known’, one SH2 domain

Two of the three forms of SHIP contain would

for its

suggested

in part for the reduchon signahng

the interaction

and al1 three forms encode

phospholy!ated,

ITIM and by recmihnent

to exert its effects. It was also pm-

and may account during

the sites of tymsinr

one PTl3 domam.

from several IaburatoriesU

monsti-

of SHIP may be responstble

basis underlying

and She is not well understood

in negative signaling

F&II

of SHIP may piay a” equally

the site(s) on SHIP are unknown. R.xe”t experiments

upon activation,

play a key role in negative

the phosphorylated

to negative

the noncovalent

though SHIP

interaction

of lIA1.6 with cDNA encodmg

speahc

In support

in this re-

IlA1.6 B cells did not undergo

toted bath events-“. On the basis of these results, i! was pmposed”

ation, induced by co-ligation of the EKE and FcyRll, and leading to remitment and biding of SHP-I, which then dephosphorylates substrates.

played a critical role in

Indeed, recent experiments

that FqRlldeficient

SHIP phosphorylation

with She.

of cells with anti-FqRll

and

a single

two NPxY sites that, when for PTB domains.

Indeed,

I997

IMMUNOLOGY

/’

Positive

TODAY

~rgnalmg residue

of She. I” any case, a role for the

SH2 domain terxbo”

of SHIP in the SHIP-She

iyils reported

of lnterleukl” Similarly,

3 (IL-3)sbmul&d

experiments

t

a r”le both

binding

paradigm

expenments triggering

to phos-

in T cells respondmg have indicated

mteraction mai”

bmdmg

SHIP,

She (Ref 40). Bv contrast,

phorvlated

+ MEK

have

for the She PTB de

to NPxY motifs within

and the SHIP SH2 domam,

Raf

celis~-“.

using the B cell posi-

hve- and negatives~gnaling in&cated twin,

mwlwd

Thus. the precise

the SHIP SH2 doma”?.

mode of the SHIP-She

may depend

tem under

the She PTB do

the NPxY motif of SHIP

and &d not “wolve terxtion

recent to CD3

that the SHIP-She

only

recognizing

in-

in hvo recent studies

study, the stoichiomehy

phosphorylation,

in-

on the signaling

other

protein

sys-

of SHIP

interactions

of SHIP and She, and ‘or other unknown ramelrs. ditions

Nevertheless, of negative

pa-

in B cells under con-

sigtlaling,

the SHZ do-

mams of both Grb? and SHIP are able to bind phosphc-She,

which raises the possibiity

one may bind to thv exdusion

Recent experiments tivity

under

in 6 cells have demonstrated

negative

sigraling

conditions”.

tion of Raf-1, a serine/thrwnine

k&se

hve signaling

condlhons.

both dnu?s+-m restored

upon

rqative reduchon earlier

under

condit;Lns

the Ras pathway

ho” of the SH2 domains (Frg. 2). A mwkl

direct competition

can only involve

Whde ihe competihon from

ative stgnahng frog oocytes

model

several

for the reduced cannot

be excluded.

lion of a catalyrically

deficient

bebpen

of She

SI-hP and

forms of the erqme.

other

above

potential

For example,

is supported influences

of the Ras pathway

that microinjection

insulin-mduced

during

to “eg-

recent studies of catalytically

iXK activity,

of ac-

while mrroinjec-

form oL SHIP did not+‘; this suggests

a potenhal mIe for SHIP enz)rmatic acta\ & m bixking 5HP-1 may contribute

with

reduction

the 145 or 135 kl;z forms of

summarized

sourclfs.

activation

have indicated

tive SHIP block&

together

may be due to competi-

SHIr s111cethese are the SH2-donvdn-contai”ing by findings

and a concomitant

that the obsewxl

signaling

was

Similarly,

m SHIP phos-

of SHIP and Grb2 for phosphoryiated

involvmg

Grb2 for phospho-She

account

anhbcdy.

These findmgs,

the ““ho6

of Ras and

co-cmsslinking

anti-FqRII

led to a” increase

negative

but not posi-

the rnduchon

BCR-F-R

intewtion”.

during

downstream

kinase downsheam negahve

higher lewls of SHIP-She interactron in Shc-GrbZ

datrZ-‘“, support

Ras ac-

the induc-

immediately

under

Furthemmre.

ktnases

ti.m use of blochng

signaling

phorylation,

reduced

reduced

Siiilarly,

of Ras (Ref. 42) and of ERK. a serine/threonine of Raf (Ref. 433). was greatly

that

of the other.

to the block tn Ras induchon

Ras inductIon. during

negative

IMMUNOLOGY

TODAY