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* AXA's Henri De Castries says to step down
* Speculation that Castries could chair HSBC
* AXA names German-born Thomas Buberl as new CEO (Adds de Castries comments)
By Maya Nikolaeva
PARIS, March 21 (Reuters) - AXA Chief ExecutiveHenri de Castries will step down in September after nearly 17years at the top of Europe's second-largest insurer, fuellingspeculation that his next role could be as HSBC chairman.
Castries, who joined AXA in 1989, has spent the past fiveyears expanding the group's business into emerging markets witha 5.1 billion euro ($5.7 billion) acquisition spree in Asia,Latin America and Africa.
In a letter to staff announcing his departure, Castries, 61, said "it is only natural that a new team launches and managesour new strategic plan to be announced in June 2016".
Thomas Buberl, 42, who heads AXA's German business, has beenappointed deputy chief executive and will take over fromCastries when he leaves in September.
AXA is also splitting the chairman and CEO roles. Thecurrent deputy CEO in charge of finance, Denis Duverne, 62, willreplace Castries as chairman.
Castries' departure is the latest in a series of leadershipchanges at European insurers, with Prudential, Zurich, Old Mutual and Munich Re allannouncing new CEOs in the past year.
Under a five-year strategic plan completed last year, AXAconsolidated its position as Europe's second-biggest insurerafter Germany's Allianz by trimming its exposure tomature markets and increasingly focusing on faster-growingemerging markets where insurance coverage remains low.
HSBC SPECULATION
Castries is seen as a front-runner to take over from DouglasFlint as HSBC chairman, having joined the bank's board lastyear. HSBC said last week that it had begun to look for areplacement for Flint and expected to nominate someone in 2017.
"I think Henri de Castries is quite likely to replace Flint,(I) have been hearing that for the last nine months," one HSBCshareholder told Reuters, on condition of anonymity.
"He is in a learning phase now and could step up next year".
HSBC said it did not comment on speculation.
Castries tried to dampen the speculation, saying peopleshould not read too much into the timing of the announcement ofmanagement changes at AXA and HSBC.
"I know there is some sort of fantasy that I saw thismorning regarding HSBC," Henri de Castries told journalists.
"I haven't taken part in a single board meeting at HSBC yet,I will do that next month...I'm a board member. I'm proud of it,that's it".
GERMAN-BORN BOSS
Incoming CEO Buberl is expected to focus on shareholderreturns and changes in digital technology, a London-basedanalyst said.
"AXA is in very good shape at the moment, with a strongbalance sheet...The first challenge is to keep what we havetoday," Buberl told journalists.
Buberl would be a rare foreign boss among leading Frenchcompanies. He was born in the German town of Wuppertal andeducated in Germany, Britain, and Switzerland.
Since joining AXA in 2012, he has led the group's life andsavings business, and health line. Previously he worked at theWinterthur group, which was acquired by AXA in 2006, and ZurichInsurance Group. ($1 = 0.8881 euros)
(Additional reporting by James Regan, Leigh Thomas in Paris andSinead Cruise in London; Editing by Andrew Callus and KeithWeir)
